Add Timelog: show the timer in the tab title and simplify the code

This is the first commit of the project, at the state that runs on
timelog.minhtrannhat.com.

Changes in this state:
- Remove redundant UI text from the sidebar, timer and insights pages.
- Show the remaining time and tag in the browser tab title while a
  session runs.
- Put the shared record type and the due and end helpers in
  src/shared/record.ts.
- Remove the startup tag migration and the one-time Forest import
  script. The live data does not need them.
- Remove unused CSS, Playwright ignore rules and duplicate helpers.
- Do not track Forest CSV exports, because they contain private data.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

.env.example

@@ -0,0 +1,14 @@
+# Public URL, including https:// and no trailing slash.
+PUBLIC_ORIGIN=https://timelog.minhtrannhat.com
+
+# Create a GitHub OAuth app with callback:
+# https://timelog.minhtrannhat.com/auth/github/callback
+# The ID is the stable numeric account ID from https://api.github.com/users/YOUR_LOGIN.
+GITHUB_CLIENT_ID=
+GITHUB_CLIENT_SECRET=
+GITHUB_ALLOWED_ID=
+
+# Generate these with: bun run vapid
+VAPID_PUBLIC_KEY=
+VAPID_PRIVATE_KEY=
+VAPID_SUBJECT=mailto:[email protected]