Enables `[claude] extra_args = ["--chrome"]` so Untether-spawned Claude
Code sessions can opt into the Claude-in-Chrome extension — previously
the `mcp__claude-in-chrome__*` tool namespace was absent from Untether
sessions because Claude Code 2.1.x gates it behind `--chrome` /
`CLAUDE_CODE_ENABLE_CFC=1`, and Untether never passed the flag.

Mirrors `codex.extra_args` and `pi.extra_args`. Flags Untether manages
internally (`-p`, `--print`, `--output-format`, `--input-format`,
`--resume`/`-r`, `--continue`/`-c`, `--permission-mode`,
`--permission-prompt-tool`) are rejected at config-load with a
`ConfigError` so duplicate-argv surprises fail fast. User args land on
argv after the managed stream-json prelude and before resume / model /
effort / allowed-tools / permission flags, preserving the trailing
`-p <prompt>` (or stdin prompt under permission-mode) position.

- src/untether/runners/claude.py: add `extra_args` field, thread
  through `build_args`, parse + validate in `build_runner`
- tests/test_build_args.py: +8 tests (argv ordering, permission-mode
  argv, multi-flag order, build_runner parsing, reserved-flag rejection
  for individual flags and `key=value` prefixes)
- docs/reference/config.md, docs/reference/runners/claude/runner.md:
  document the new key, including reserved-flag list
- CHANGELOG.md: v0.35.3 (unreleased) entry

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

…dovers

Public repo hygiene pass. Three classes of file shouldn't be committed
going forward:

1. docs/handover/ (new) — Claude Code handover docs that pass context
   between sessions. Internal-only by nature.
2. docs/audits/ — incident and security audits referencing production
   bot names and internal workflows. GitHub issues/milestones are the
   public tracker.
3. docs/tests/ — per-release integration test plans and execution
   reports. Contain internal bot references, skipped-test notes, and
   QA methodology detail that isn't user-facing. docs/reference/
   integration-testing.md remains the public playbook.
4. incoming/*.md — draft design and feedback markdown uploaded via
   Telegram file-transfer. Auto-named file_*.jpg already covered.

Files untracked (contents preserved on disk):
- docs/audits/pitchdocs-context-guard-interference.md
- docs/tests/v0.35.2-integration-test-plan.md
- docs/tests/results/v0.35.2-results.md
- docs/tests/results/v0.35.2rc3-results.md

mkdocs/zensical nav (zensical.toml) doesn't reference any of these
paths, so the docs site build is unaffected.

History note: these files remain visible in git history; removing
them entirely would require a separate BFG/filter-branch pass, which
is out of scope for this PR. The forward-going commitment is that
internal planning/audit/test-artifact content stops being tracked.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>