[vitalNohj]

Closes #279

Shows a session the device kept as soon as the page can check it, on a reload and on a first visit, instead of waiting for the sign-in check and then jumping to it.

What it does

• A signed-in page carries who is signed in and which build, so a session the device kept can be checked and shown before /api/me answers. A signed-out page, and a server that does not keep sessions on the device, carry neither.
• The page stays hidden until that check finishes. With a checked copy, the session replaces the starting screen. With none, the starting screen stays until the server answers.
• The copy is checked again once /api/me answers. A changed person, rights, or build removes it, on the device too, and a later switch cannot bring it back. A startup retry checks the same copy again.
• Opening a session the device kept, but this tab has not shown, reads it before the server answers. One kept nowhere shows its own header and a quiet loader in the same pane, then fills that pane.
• Rows that arrive after a session is on screen glide to the bottom instead of jumping, including a late catch-up, a reconnect, and a reload.

Tests

• A cached reload paints its rows before /api/me, and never shows the starting screen. The session menu stays disabled until the check answers.
• A reload with nothing kept shows the starting screen until /api/me, then the rows.
• A switch reads rows kept only on the device before the server answers. One kept nowhere keeps its header and a loader, then fills the same pane.
• Wait for updates still holds a changed tab-memory view until the server answers.
• Another person's device copy is refused before /api/me. The page's identity is escaped, and absent when signed out or when the device cache is off.
• /api/me changing the person removes the early view and cannot keep it for a switch.
• A startup retry keeps a still-usable early snapshot, and drops one after the person changes.
• A blocked module still reveals the startup error on a signed-in page.
• A catch-up that arrives after the old window glides and does not jump, including one taller than the screen, one after a reconnect, and one after a reload. A reader scrolled up keeps the same row.

npm run check passes. eslint and prettier pass on the touched files. node --test --test-concurrency=2 on test/session-open-ui.test.ts, test/session-glide-ui.test.ts, test/design-transcript.test.ts, test/file-reopen-ui.test.ts, and test/session-cache-signout-ui.test.ts: 23 tests, 23 pass.