chore: repo hygiene — stale gitignore entries, finished plans, superseded research, doc drift

Removed (all recoverable from git history):
- llm_provider_switch_plan.txt: 2026-08-08 DeepSeek/Anthropic multi-provider plan that
  was never implemented (llm_client.py is DeepSeek-only, no `anthropic` anywhere)
- docs/superpowers/specs/2026-07-21-centralized-config-design.md: spec of the
  config.json migration that merged the same day; its plan sibling was already
  deleted in b936d44. app_config's docstring pointer goes with it.
- scripts/compare_oanda_tiingo.py: Phase 0 recent-tail smoke test, superseded by the
  Phase 1/2 study scripts (result recorded in the test plan)
- backtest/research/fetch_oanda_m15.py + oanda_td_divergence.py + its by-hour CSV:
  the 2026-07-24 Oanda-vs-Twelve-Data study, superseded by the 2026-08-14 feed
  divergence report (which keeps a one-line citation)
- backtest/research/burst_profile.py and hour_analysis.py: superseded by burst_map.py
  and book_report.py
- backtest/research/panel_payload_drytest_2026-08-15.py: one-off live DeepSeek probe;
  its .jsonl evidence stays

Added to git: the three 2026-08-14 research reports (feed divergence, re-pin
verification, signal parity), their CSV, and docs/data_source_change_test_plan.md -
CLAUDE.md cites them as standing evidence and their driver scripts were already
committed. The test plan no longer refers to auto-execution.

Hygiene:
- .gitignore: drop oanda_state.json (daemon removed 2026-09-03) and the vanished
  backtest/trailgrid dirs; ignore .coverage
- docs/architecture_diagram.py only writes the PNG when run as a script (it used
  to plot on import); test box refreshed to 461 tests / 31 modules; PNG regenerated
  (the committed one still drew the removed daemon)
- backtest/instructions_for_backtest.txt: manual-journal head replaced by the
  actual reporting checklist; the 2026-09-06 addendum is unchanged
- doc drift: README/publisher list all six published files; news_summary.php says
  4 h (not 24 h) and drops the pre-id sha1 fallback whose window closed;
  analyze_signal_log lists six lenses and --scan-outcomes; agent_panel cost model
  says 4 requests by default; tiingo comment cites the NY-anchored weekend;
  Module 21 title no longer says "execution lifecycle"

Suite: 461 passed, 0 failed.

Claude-Session: https://claude.ai/code/session_0156YhogLytzj9P2iH1skGbL

backtest/research/feed_divergence_oanda_vs_tiingo.csv

@@ -0,0 +1,2 @@
+tf,a,b,a_bars,b_bars,common,a_only,b_only,dir_agree_pct,ret_corr,mean_abs_dclose,p95_abs_dclose,max_abs_dclose,dclose_pct_atr_mean
+5min,oanda,tiingo,70901,73241,70807,94,2434,97.674000,0.994970,0.123070,0.285000,26.105000,2.147942