docs: refresh scout README to house style - #25

What changed (docs only)

Rewrote README.md to the family house style — tight, skimmable, every command verified against the current code (compose.yaml, scripts/, app/main.py, scout/, evals/, example.env):

• New structure: tagline → intro → How it works → Quick start → Interfaces → Deploy → Configuration → Evals → Source/links.
• How it works: consolidated the agent + context-provider explanation and the provider table (verified against scout/contexts.py); dropped the YC RFS framing.
• Quick start: unchanged compose path, verified against compose.yaml (scout-db + scout-api, port 8000, hot reload).
• Interfaces: now covers all three wired interfaces — AgentOS web UI, Slack (both env vars required for the interface; token alone gives the read-only context), and the terminal CLI (python -m scout / python -m scout contexts, verified against scout/__main__.py). Kept both demo videos.
• Deploy: condensed the 7-step Railway walkthrough into a pointer with the two must-know facts: JWT_VERIFICATION_KEY required at prod boot (agno 2.7 / authorization=runtime_env == "prd" in app/main.py), and the single-replica scheduler caveat. Removed the hardcoded app/main.py:67 line reference (brittle).
• Configuration: env-var table sourced from example.env (no secret values).
• Evals: commands verified against evals/__main__.py (wiring, default behavioral, --case, judges).
• Removed the stale What's next section (referenced unmerged feat/slack-interface work) and other prose drift.

CONTRIBUTING.md does not exist; docs/*.md checked and found current (WIKI_GIT.md already documents the GitBackend auto-detect) — no changes needed there.

Non-doc issues spotted (NOT changed in this PR)

1. Scheduler vs. replicas: railway.json sets numReplicas: 2 while app/main.py enables scheduler=True. The AgentOS scheduler assumes a single replica — with 2 replicas scheduled tasks can fire twice. README now documents the caveat, but the config itself may want numReplicas: 1 (or a leader-election story).
2. Stale comment in example.env (wiki section, ~line 66): says "Then update _create_knowledge_wiki() in scout/contexts.py" — obsolete since the GitBackend auto-detect landed (89090b5). Left untouched to keep this PR strictly docs; trivially fixable in the open bump PR or a follow-up.
3. requirements.txt pins agno==2.6.4; the README's "agno 2.7 requires JWT_VERIFICATION_KEY at prod boot" claim anticipates the open chore/update-* bump PR. Worth double-checking the wording lands after/with that bump.

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