revert(*): back out the web settings timezone write fix

[gloryfromca]

Summary

Reverts #506. The fix it carried edits ui-web/src/features/settings/SettingsPage.tsx,
a file the ui-web rebuild on refactor/ui_web_architecture (#475) replaces with
SettingsApp.tsx and its pages/ tree, so the frontend half cannot travel across
that rewrite. The backend half goes with it so the change stays one reviewable unit:
it is redone on the refactor branch instead, where the settings page it has to edit
actually exists. #506 carries a note asking its author to resubmit there.

Nothing else landed on main between #506 and this revert, so the result is the
pre-#506 tree exactly.

Type

• Fix
• Feature
• Docs
• CI / tooling
• Refactor
• Other (revert)

Verification

git diff --stat 04eb8a31d 9f1fd7c73 is empty: this head's tree
(00f113b27b7443562f83e89f27adcf8874c1dc91) is byte-identical to the tree of
04eb8a31d, the commit main sat on before #506 merged. The unit suite,
lint, and the contract checks ran on this head in CI rather than locally.

coverage gates is red and stays red: the diff-coverage gate scores the 11
restored lines in the cron.forwardChannels validation branch, which had no test
covering them before #506 deleted them. A revert cannot raise that number without
writing tests for code it is removing from the writable set.

• Relevant tests pass locally
• Relevant lint / type checks pass locally
• User-facing docs or screenshots are updated when needed

Risk

The web settings timezone control goes back to failing its write with
-32603 internal_error, which is the behaviour every release before #506 shipped.
Rollback is re-applying #506, or the resubmission on refactor/ui_web_architecture.

• Security impact considered
• Backward compatibility considered
• Rollback path is clear for risky changes

Related Issues

Reverts #506.

[gloryfromca]

Blocking: preserve the working timezone save and keep the retired forward-channel setting removed.

This exact revert reintroduces both failures corrected by #506. Calling settings.set at this head with ordinary values produced KeyError for both keys and left the config unchanged: the cron writer accepts Python field names while the restored RPC path passes defaultTimezone, and forwardChannels has no schema field at all. The latter also conflicts with the fire-at-origin architecture and the loader migration that strips this retired key. The focused suites remain green because this revert deletes the five regression cases that covered these paths.

Coverage: I reviewed the full github/main...HEAD diff; AGENTS.md and CLAUDE.md; CONTEXT-MAP.md and the canonical fire-at-origin guidance; the settings UI caller, RPC boundary, cron writer, schema, loader, scheduling consumers, relevant history and #506 record; backward compatibility; test strength; architecture boundaries; and current mergeability.

Verification: uv run pytest tests/test_rpc_settings.py tests/test_config_update.py tests/test_config_loader.py tests/test_cli_cron_commands.py -x (232 passed); npm test --prefix ui-web -- --run src/features/settings/SettingsPage.test.tsx (123 passed); npm run type-check --prefix ui-web (passed). A direct isolated-config invocation of settings_set reproduced KeyError for both cron.defaultTimezone = "UTC" and cron.forwardChannels = ["telegram"], with {} still on disk.

[gloryfromca]

No blockers; suggestions only, and they are marked inline.

The tree is unchanged from the previously reviewed revision, so both measured regressions remain real. The amended PR record now explicitly accepts the temporary timezone internal_error and defers the whole #506 repair to the replacement settings implementation on #475. That author-level scope decision means neither item blocks this revert; both earlier threads have been replied to and resolved.

Named follow-up: #475's current head already omits the retired forwardChannels row from the replacement UI, but its RPC backend still passes defaultTimezone without conversion and still whitelists cron.forwardChannels. The resubmission there still needs the backend conversion/refusal and regression coverage before that branch merges.

Coverage for this revision: I reviewed the full github/main...HEAD diff and the delta from 51482dacc338; rechecked the AGENTS.md/CLAUDE.md constraints, canonical fire-at-origin guidance, callers, schema, loader, history, backward-compatibility impact, removed tests, architecture boundaries, amended PR record, and the stated #475 follow-up branch. The new commit changes attribution/message metadata, not the source tree.

Verification: uv run pytest tests/test_rpc_settings.py tests/test_config_update.py tests/test_config_loader.py tests/test_cli_cron_commands.py -x (232 passed); npm test --prefix ui-web -- --run src/features/settings/SettingsPage.test.tsx (123 passed); npm run type-check --prefix ui-web (passed).