docs: restructure README (1205 → 497 lines) — ops-manual content moves to docs/ (#172)

Maintainer-approved P2 restructure. Principle: what a new user needs in the first
10 minutes stays in README; the operations manual moves to docs/. Content MOVED,
not rewritten — an independent verifier swept all 20 original sections, 60+
distinctive facts, and all table rows against the new corpus: zero content loss.

New files (verbatim moves + two mandated dedup merges):
- docs/lan-mode.md    (396) — LAN setup, key management, quotas, anonymous access,
                              deployment/security model + honest limits, client connect
- docs/tui-mode.md    (196) — full TUI section + the four giant env-cell essays as
                              prose subsections; opens with the single-user SECURITY
                              warning + the PAUSED billing-split status banner
- docs/troubleshooting.md (136) — full troubleshooting; canonical 401/credential-
                              isolation explanation (union of the 4 prior copies)
- docs/upgrading.md   (79)  — upgrade paths, snapshots, rollback, auto-sync

README keeps: pitch (byte-identical), new TOC, 62-line Quickstart, How It Works
verbatim (incl. #171 billing-status note + workload fit), the three release_kit-
pinned tables (Available Models / API Endpoints / all 37 Environment Variables
rows — 4 giant TUI cells now one-line pointers), All Commands, slim Troubleshooting
(bootstrap quirks retained per release_kit bootstrap_quirk_policy), summary stubs
linking each moved doc, Repository Layout (+4 doc rows), Governance, Support.

Dedup (canonical copies): sdk-cli vs subscription-pool table → docs/tui-mode.md;
credential-isolated-home / permanent-401 → docs/troubleshooting.md#tui-401.
Link retargets: docs/runbooks/615-canary.md, docs/runbooks/tui-flip-rollback.md,
setup.mjs (one banner string; node --check clean). 126 links across the touched
files verified resolving; repo-wide grep shows no reference to a removed anchor.

npm test: 332 passed / 0 failed.

Co-authored-by: dtzp555 <dtzp555@gmail.com>
Co-authored-by: Claude <claude-opus-4-8> <noreply@anthropic.com>

setup.mjs

@@ -334,7 +334,7 @@ if (OPENCLAW_PRESENT) {
     `║  Aider / OpenClaw) at:                                       ║`,
     `║    http://${BIND_ADDRESS}:${String(PORT)}/v1${" ".repeat(Math.max(0, 47 - BIND_ADDRESS.length - String(PORT).length))}║`,
     `║                                                              ║`,
-    `║  See README § "Client Setup" for per-IDE instructions.       ║`,
+    `║  See docs/lan-mode.md for per-IDE client setup.              ║`,
     `║                                                              ║`,
   );
 }