feat(shell): add interactive cya shell session (CYA-WP-0007)

Implement the full interactive shell REPL with session persistence,
opt-in capped/redacted shell history, State Hub orientation and
explicit slash-command writes, orchestrator/safety wiring, end-session
learning hooks, weakness hints, docs, and tests.

docs/cya-shell-operator-session.md

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+# Example Operator Session
+
+This example uses offline mode and skips remote hub calls for a local smoke.
+In normal repo work, omit `--no-hub` so the shell reads State Hub orientation.
+
+```text
+$ cya shell --offline --no-hub
+cya shell
+Session: cya-20260623-101500-1a2b3c4d
+Artifact: ~/.config/cya/sessions/cya-20260623-101500-1a2b3c4d.jsonl
+
+State Hub remote orientation not available.
+History lines: 0
+
+Type /help for commands, /exit to finish.
+cya> summarize what changed in this repo
+... standard orchestrator response ...
+cya> /explain
+... context envelope, memory, shell history status, hub summary, and hints ...
+cya> /hub
+... active workstreams or offline notes ...
+cya> /export-session
+Exported session summary: ~/.config/cya/sessions/cya-...-summary.json
+cya> /exit
+Session saved: ~/.config/cya/sessions/cya-...jsonl
+```
+
+For history-aware continuity, opt in explicitly:
+
+```bash
+cya shell --with-history
+```
+
+The history context is capped, redacted, and shown in `/explain`. Secret values
+should still be routed through the approved custody path, not pasted into the
+session.
+
+State Hub writes require a slash command and interactive confirmation:
+
+```text
+cya> /hub log "Implemented CYA-WP-0007 shell skeleton and tests"
+Post progress note to http://127.0.0.1:8000? [y/N]: y
+```