chore: drop unreferenced maintenance scripts and self-contained web comments (#171)

## Related Issue

No issue — housekeeping found while reviewing what the repository
publishes.

## Problem

Two unrelated pieces of cruft, both harmless to runtime and both
misleading to read:

1. `scripts/upstream-sync/` held maintenance scripts that nothing in the
repository referenced — no workspace script, no CI job, no import. They
were tracked, so every clone shipped them and every reader had to work
out whether they mattered.
2. Around fifty comments under `apps/pythinker-web` documented their own
behaviour by comparison to things that do not exist in this repository —
symbols no file here defines, artifacts no build here produces, and
opaque release markers like `S1 parity`. A comment a reader cannot
follow or check is worse than no comment: it looks authoritative, and
there is no way to tell whether it is still true. Two local identifiers
(`ReferenceTaskItem` / `referenceTask`, duplicated in `TasksPane` and
`SubagentGrid`) carried the same unresolvable meaning in code rather
than in a comment.

## What changed

- Removed `scripts/upstream-sync/`.
- Rewrote the affected comments and doc lines to state what the code
does on its own terms: what the component renders, what the splitter
clamps to, why the picker keeps focus. Every claim is now checkable
against a file in this repository.
- Renamed the two local helpers to `ExtendedTaskItem` / `extendedTask`
in both files that defined them.
- Rebuilt the committed web bundle, because editing the sources changes
the fingerprint the packaging gate checks.

No behaviour changes: outside the generated bundle and the two local
renames, the diff is comments and Markdown.

## Checklist

- [x] I have read the
[CONTRIBUTING](https://github.com/PyModel/pythinker-code/blob/main/CONTRIBUTING.md)
document.
- [ ] I have linked a related issue (external PRs: the issue must have a
maintainer's `/approve`).
- [ ] I have added tests that prove my feature works. — no behaviour
change to test.
- [x] Ran `gen-changesets` skill, or this PR needs no changeset. — no
changeset: nothing here is user-perceivable.
- [x] Ran `gen-docs` skill, or this PR needs no doc update.

## Verification

`pnpm run typecheck` 0 · `pnpm run lint` 0 errors · web 939/939 ·
`check-nix-workspace.mjs` 0.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Expanded code editor support for TypeScript, XML, YAML, and related
language services.
- Added rendering support for additional diagram types, including
Sankey, timeline, state, swimlane, Venn, Wardley, and XY charts.
  - Added improved diagram sizing capture for more accurate rendering.

- **Refactor**
- Refreshed web assets and build outputs for the latest editor and
diagram capabilities.

- **Documentation**
- Clarified interface behavior and removed outdated implementation
references.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: elkaix

apps/pythinker-code/dist-web/.web-bundle-manifest.json

@@ -1,4 +1,4 @@
 {
-  "sourceHash": "18d708358b92ec6e3ca36beb9975132d720096a6d1812ff94f0b3ec97ce45803",
+  "sourceHash": "a99e6d017b3b0411cf2f7f4573234f80e7085afb05ad65a58d20642184cf0c38",
   "sourceFileCount": 390
 }