feat: add quotations from marked text, with citations and sharing

SPEC.md

@@ -81,12 +81,13 @@ The v1 client presents one reader screen:
 - A web page that cannot be loaded offers to open in the reader's system web browser, since the web can be shown outside; a page over gemini or spartan has nowhere else to go, so its failures offer only trying again.
 - On pointer hosts the keyboard drives the reader: Ctrl or Cmd+L focuses the address field with its text selected, Ctrl or Cmd+R reloads the page, and the walk goes back and forward with Alt+Left and Alt+Right, or on a Mac with Cmd+Left, Cmd+Right, Cmd+[ and Cmd+]. Touch devices navigate with gestures instead, and none of these shortcuts are offered there. The links on a page are reachable by keyboard as well: the page is one stop in the focus order, and once it holds the focus, Tab highlights its links in reading order and Enter opens the highlighted one; the page scrolls to keep the highlighted link in view, Shift+Tab walks back, Escape puts the highlight away, and a Tab past either end hands the focus back to the chrome.
 - A swipe right goes back and a swipe left goes forward through the history stack. On a pointer host the whole empty margin beside the text column accepts the swipe, with a 40 px floor, so the gesture stays clear of selecting text, and the address bar's buttons work as well. On a touch device, where the column leaves no margin, the page surface itself accepts the swipe: a finger that crosses the slop sideways, before the long press that starts a text selection completes, is swiping, while a finger that held still that long keeps its drag for the selection.
-- The client's own pages live under the `mews:` scheme. `mews:hub` names them and says what each one holds; `mews:posts`, `mews:bookmarks`, `mews:subscriptions`, `mews:history` and `mews:settings` each carry a strip linking to the others. Bare `mews:` is the hub, and the hub is where a session with no history to return to starts. Each page is built as an ordinary Mews document and rendered by the same renderer as a fetched page, so it joins the history stack and the swipe transitions, and none of them is recorded in history or offered for subscription.
+- The client's own pages live under the `mews:` scheme. `mews:hub` names them and says what each one holds; `mews:posts`, `mews:quotations`, `mews:bookmarks`, `mews:subscriptions`, `mews:history` and `mews:settings` each carry a strip linking to the others. Bare `mews:` is the hub, and the hub is where a session with no history to return to starts. Each page is built as an ordinary Mews document and rendered by the same renderer as a fetched page, so it joins the history stack and the swipe transitions, and none of them is recorded in history or offered for subscription.
 - `mews:posts` is every post from every subscribed site in one list. The reader can order it by date, by site, or unread first, and limit it to unread posts; those choices ride in the address as a query string, so going back undoes one and a swipe preview shows the page the reader will land on. Unread posts are shown bold, and opening a post marks it read.
 - A site that publishes through an Atom feed instead of dated links is read through the feed (spec 6.2). Dated links are the normative mechanism, so the feed is only asked for when the page itself listed nothing, and a feed on another site is refused. Posts are keyed by address, so a post listed both ways is stored once, under the title the page gave it.
 - Subscribed sites are checked once in the background at launch, and whenever the reader asks. Sites are checked one after another rather than at once, and a site that cannot be reached keeps the posts already held and is still recorded as checked, so one site being down never stops the rest.
 - A fresh install comes with the project's directory of sites already bookmarked, so a first session has somewhere to go. It is a bookmark like any other: removing it is the reader's own, and no later start gives it back.
 - The reader can tag bookmarks and sites. A tag exists only while something carries it, so adding a tag and making one are the same act; `mews:tags` lists every tag in use and what carries it, and following a tag narrows the list it belongs to. There is no renaming and no empty tag.
+- The reader can keep marked text as a quotation. Marking text on a page offers, in the selection toolbar, to save it; the kept text is stored with the page it came from, with the author when the page's metadata named one, and with the site's title when the reader's subscriptions know the site the page belongs to. `mews:quotations` lists what is kept, one row per quotation naming the author, the article's title and the site it came from — by its own title when the reader's subscriptions know it, by its host otherwise — with the day it was kept, ordered by that day or by the page it came from, narrowed by a search over the text, the author, the page's title and its address. A row shares its quotation through the system share sheet, together with a citation shaped as APA names a web page: the author first when the page carried one, otherwise the article's title; the year as a no-date marker, since a page declares no date; then the article's title, the site's own title (its host when the subscriptions do not know it), and the address. A row can remove its quotation, and nothing else is offered, since the citation is the record of where the words came from.
 - Each library page carries a search box that narrows it by title or address as the reader types, a quarter second after they stop. The query rides in the address as any other view state does, but it replaces the step of the walk they are standing on rather than adding one, so a search of eight letters is one step back and not eight; the box keeps what they typed as the page rebuilds under them, and follows the page when the page sets it, as clearing the search does. Submitting the box still works, for a reader who would rather say when to search. Each row carries its own actions: remove a bookmark, leave a site or check it now, forget a page. History lists one row per address, headed by the most recent visit, rather than repeating a page once per visit. Clearing history takes a second step on a page the reader can simply leave, since it cannot be undone.
 - A change is a link too: following `mews:do/<verb>` applies it and rerenders the page in place without adding a history entry. Only a link followed from one of the client's own pages is honored, so a fetched page cannot clear history or change a setting on the reader's behalf (spec 8.1). A form on one of these pages is routed the same way rather than sent to the network.
 - Our own pages are built from the same blocks as a page but are interface, not an article, so the renderer lays them out differently: wider before they stop growing, denser, rows divided by a line instead of bulleted, section headings quieter, a note under a row set smaller and dimmer, links carried by weight rather than an underline, and a one-field form on a single line.