feat: PDF sources: read, take notes and cards from pages, deadlines

PDFs live in a studyset's new Files tab: uploaded from Add material
(a file the studyset holds already asks first), each row with its
pages, cards, notes and size, how far it is read and its reading
deadline; renamed, given a deadline (a page or a chapter by a day),
marked as read, started afresh, deleted with a moment to undo.

The reader (/pdfs/:id) opens where reading left off: on wide windows
a rail of tools (search, fit, zoom, fullscreen), a page counter with
the chapter, and a sidebar; on phones a top bar, a page scrubber and
a sheet. The sidebar holds the PDF's flashcards, by page or chapter,
made from selected text or written there, each tied to its page and
tagged with its chapter; and the page's note, an ordinary note tied
to the page. Screenshots of a region become images that know their
page. Cards and screenshots lead back to their page; reading on past
a chapter with cards suggests studying it. Home shows the deadlines
running and to come, and a timeline of them.

Server: pdf_source rows (content in the payload, last writer wins)
and an append-only pdf_reading log, the furthest page derived from
it so devices never conflict. Files up to 50 MB for PDFs (20 MB for
others; a larger file that isn't a PDF is deleted once stored). A
deleted PDF takes its file's asset row along unless another PDF has
the same file. Card payload 4 and note payload 2 keep the page.

The reader draws with pdfrx (PDFium) behind PdfEngine in
Dependencies; widget tests use a fake, and
integration_test/pdf_engine_test.dart checks the real engine on a
device or the desktop.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_server/migrations/20261003110855698-pdf-sources/migration.sql

@@ -0,0 +1,140 @@
+BEGIN;
+
+--
+-- Function: gen_random_uuid_v7()
+-- Source: https://gist.github.com/kjmph/5bd772b2c2df145aa645b837da7eca74
+-- License: MIT (copyright notice included on the generator source code).
+--
+create or replace function gen_random_uuid_v7()
+returns uuid
+as $$
+begin
+  -- use random v4 uuid as starting point (which has the same variant we need)
+  -- then overlay timestamp
+  -- then set version 7 by flipping the 2 and 1 bit in the version 4 string
+  return encode(
+    set_bit(
+      set_bit(
+        overlay(uuid_send(gen_random_uuid())
+                placing substring(int8send(floor(extract(epoch from clock_timestamp()) * 1000)::bigint) from 3)
+                from 1 for 6
+        ),
+        52, 1
+      ),
+      53, 1
+    ),
+    'hex')::uuid;
+end
+$$
+language plpgsql
+volatile;
+
+--
+-- ACTION CREATE TABLE
+--
+CREATE TABLE "pdf_reading" (
+    "id" uuid PRIMARY KEY DEFAULT gen_random_uuid_v7(),
+    "spaceId" bigint,
+    "pdfSourceId" uuid NOT NULL,
+    "readAt" timestamp without time zone NOT NULL,
+    "kind" text NOT NULL,
+    "page" bigint NOT NULL
+);
+
+-- Indexes
+CREATE INDEX "pdf_reading_space_idx" ON "pdf_reading" USING btree ("spaceId");
+CREATE INDEX "pdf_reading_source_idx" ON "pdf_reading" USING btree ("pdfSourceId", "readAt");
+
+--
+-- ACTION CREATE TABLE
+--
+CREATE TABLE "pdf_source" (
+    "id" uuid PRIMARY KEY DEFAULT gen_random_uuid_v7(),
+    "spaceId" bigint,
+    "studysetId" uuid NOT NULL,
+    "keyId" text,
+    "payload" bytea NOT NULL,
+    "nonce" bytea
+);
+
+-- Indexes
+CREATE INDEX "pdf_source_space_idx" ON "pdf_source" USING btree ("spaceId");
+CREATE INDEX "pdf_source_studyset_idx" ON "pdf_source" USING btree ("studysetId");
+
+--
+-- ACTION CREATE FOREIGN KEY
+--
+ALTER TABLE ONLY "pdf_reading"
+    ADD CONSTRAINT "pdf_reading_fk_0"
+    FOREIGN KEY("spaceId")
+    REFERENCES "offline_sync_spaces"("id")
+    ON DELETE CASCADE
+    ON UPDATE NO ACTION;
+ALTER TABLE ONLY "pdf_reading"
+    ADD CONSTRAINT "pdf_reading_fk_1"
+    FOREIGN KEY("pdfSourceId")
+    REFERENCES "pdf_source"("id")
+    ON DELETE CASCADE
+    ON UPDATE NO ACTION
+    DEFERRABLE INITIALLY DEFERRED;
+
+--
+-- ACTION CREATE FOREIGN KEY
+--
+ALTER TABLE ONLY "pdf_source"
+    ADD CONSTRAINT "pdf_source_fk_0"
+    FOREIGN KEY("spaceId")
+    REFERENCES "offline_sync_spaces"("id")
+    ON DELETE CASCADE
+    ON UPDATE NO ACTION;
+ALTER TABLE ONLY "pdf_source"
+    ADD CONSTRAINT "pdf_source_fk_1"
+    FOREIGN KEY("studysetId")
+    REFERENCES "studyset"("id")
+    ON DELETE CASCADE
+    ON UPDATE NO ACTION
+    DEFERRABLE INITIALLY DEFERRED;
+
+
+--
+-- MIGRATION VERSION FOR halkyon_learn
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('halkyon_learn', '20261003110855698-pdf-sources', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20261003110855698-pdf-sources', "timestamp" = now();
+
+--
+-- MIGRATION VERSION FOR serverpod
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('serverpod', '20260824182259319', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20260824182259319', "timestamp" = now();
+
+--
+-- MIGRATION VERSION FOR serverpod_auth_idp
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('serverpod_auth_idp', '20260924105404509', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20260924105404509', "timestamp" = now();
+
+--
+-- MIGRATION VERSION FOR serverpod_offline_sync
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('serverpod_offline_sync', '20260914143806119', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20260914143806119', "timestamp" = now();
+
+--
+-- MIGRATION VERSION FOR serverpod_auth_core
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('serverpod_auth_core', '20260924105232991', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20260924105232991', "timestamp" = now();
+
+
+COMMIT;