docs: AGENTS.md + evidence-backed scaffold (state, trials, decisions, handoff)

- AGENTS.md operating rules incl. Gitea SSH port-2222 note + known_hosts incident
- CURRENT_STATE / TODO / CHANGELOG / TRIALS
- trials: endpoint-key pairing; config-merge safety matrix 14/14 (verify.sh + output)
- docs: DECISIONS (mcode 0.6.12 bundle facts, digest-pinned), FEATURE-MATRIX, PROJECT-HANDOFF
- handoffs: TEMPLATE + 2026-10-19 initial-install record

trials/README.md

@@ -0,0 +1,11 @@
+# trials
+
+Bounded experiments. One directory per trial: `trials/<topic>-<YYYY-MM-DD>/` containing
+`record.md` and, where possible, a re-runnable `verify.sh` plus its captured `output.txt`.
+
+Required sections: question/hypothesis, scope + acceptance criteria, inputs (paths,
+hashes, tool versions), procedure (exact commands), expected vs observed, evidence
+paths, verdict (`confirmed` / `rejected` / `inconclusive` / `blocked`), and a repeat
+guard (what would justify another attempt). Preserve failed runs.
+
+Index lives in `TRIALS.md`. Routine edits and ordinary test runs do not need a trial.