release: bump to v1.6.2, docs cleanup

Promote [Unreleased] CHANGELOG entries to [1.6.2]. Bump all version
strings (pyproject.toml, server.json, __init__.py, api/main.py). Remove
stale April planning doc from git tracking. Add dashboard-design.md to
docs index. Update releasing.md to reflect current state.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

docs: document MCP setup and release status

fix: shorten server.json description to fit MCP Registry 100-char limit

Co-Authored-By: Claude Opus 4.7 <[email protected]>

chore: update llms.txt/full for v1.4.0 (14 providers, Wolfram, Yahoo)

chore: bump version to 1.3.2

Co-Authored-By: Claude Opus 4.6 <[email protected]>

chore: add CI workflow, CHANGELOG, SECURITY.md, CI badge

- CI: pytest on push/PR across Python 3.11-3.13
- CHANGELOG.md: v1.0 through v1.3.1 from git history
- SECURITY.md: supported versions, vulnerability reporting, SSRF
- README: add CI workflow badge
- GitHub topics: mcp-server, search-api, search-broker, web-search, etc.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

feat: add 3 providers, 2 extractors, tier-based credit routing (v1.3.0)

New search providers:
- Linkup (POST api.linkup.so, tier 1 monthly, 1k queries/mo)
- Parallel AI (POST api.parallel.ai, tier 3 one-time, 16k credits)
- You.com (GET api.you.com, tier 3 one-time, $100 credits)

New extractors:
- Crawl4AI (self-hosted JS rendering, no API cost)
- You.com Contents API ($1/1k pages, uses search key)

Tier-based credit-aware routing:
- Tier 0 (free/unlimited): SearXNG always first
- Tier 1 (monthly recurring): Brave, Tavily, Exa, Linkup
- Tier 3 (one-time credits): Serper, Parallel, You.com last
- Mode-specific ordering preserved within each tier
- Budget enforcement skips exhausted providers automatically

Co-Authored-By: Claude Opus 4.6 <[email protected]>

chore: rename package to argus-search, bump to 1.2.1

PyPI name conflict — 'argus' is taken by an unrelated project.
argus-search is the published package name.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

ci: add PyPI publish workflow, bump version to 1.2.0

PyPI publishes automatically on GitHub release creation (not just tags).
Uses Trusted Publisher (OIDC) — no PyPI token secret needed.

Co-Authored-By: Claude Opus 4.6 <[email protected]>