Follow-up to #2336 (umbrella) / PR #2463 (partial sweep). Covers Area 3 deferred from that PR.

Scope

Remove thinkingLevel from SessionEntry and all its reading/writing surfaces:

• src/config/sessions/types.ts — delete thinkingLevel from SessionEntry.
• src/gateway/protocol/schema/sessions.ts — delete the gateway protocol schema field.
• src/config/types.agent-defaults.ts:177 (approximate) — delete the /think comment and any default field.
• src/auto-reply/reply/session.ts — remove persistedThinking local and its read/write of entry.thinkingLevel (lines ~236, ~368, ~384, ~434).
• src/gateway/server-methods/chat.ts:778-784 — remove thinkingLevel from chat.history response payload.
• src/gateway/server-methods/sessions.ts — audit for any thinkingLevel in sessions.* response payloads / patch handling.
• src/tui/tui-command-handlers.ts, src/tui/tui.ts, src/tui/tui-session-actions.ts, src/tui/gateway-chat.ts, src/tui/tui-types.ts — remove thinkingLevel from session info / patch surface.
• src/commands/status.summary.ts — remove thinkingLevel from status summaries.
• src/acp/translator.ts — remove thinkingLevel from ACP session rows.
• src/telegram/bot-message-dispatch.ts — remove any thinkingLevel display.
• Tests: update src/config/sessions.test.ts, src/gateway/session-utils.fs.test.ts, src/gateway/server.sessions.gateway-server-sessions-a.test.ts, src/acp/translator.session-rate-limit.test.ts, src/auto-reply/reply/reply-utils.test.ts, etc.

Backward compat

Existing sessions on disk have thinkingLevel values. Since the field is optional and unread post-removal, sessions load fine (extra fields ignored) and save without it. No migration needed.

AC

• git grep "thinkingLevel" in src/ returns zero hits (allowing comments or migration-only refs if truly required).
• pnpm check + pnpm test pass.
• LIVE smoke: session patch round-trip still functional without thinkingLevel.

Context

• Parent: gut(auto-reply): finish thinking-level and model-selection sweep — follow-up to #2335 #2336 (umbrella, still open)
• Sibling shipped: PR gut(auto-reply): partial thinking-level + model-selection sweep — Areas 1+2+4 of #2336 #2463 (Areas 1+2+4)