add Alignment Forum commands: posts, post, search, tags, user

[tamnd]

Implements alignmentforum-cli (binary af) reading the Alignment Forum via its public GraphQL API.

Commands

• top -- list top-scored posts (last N days, configurable via --days)
• new -- list most recently published posts
• best -- list best-of-all-time posts
• search <query> -- full-text search with relevance ranking
• post <id> -- single post by internal ID
• user <slug> -- user profile and stats
• tags -- list curated AI safety research tags (25 entries)
• version -- version information

Design

• GraphQL API at alignmentforum.org/graphql, no auth required for public content
• Single POST per command; server returns N results in one round trip so no concurrency pool is needed
• Rate pacing (500ms default), retry on 429/5xx with linear backoff (500ms per attempt, cap 5s)
• All output via shared reflection renderer: table (TTY auto), JSONL (piped auto), JSON, CSV, TSV, URL, raw
• Exit code 3 for empty result or not found, distinguishable from error exit code 1

Tests

Four transport-layer tests using httptest.Server:

• TestGraphQLSendsUserAgent -- User-Agent header present on every request
• TestGraphQLRetriesOn503 -- 503 twice then 200, verifies 3 hits and backoff elapsed
• TestGraphQLNotFound -- null result returns ErrNotFound
• TestGraphQLErrorField -- errors array surfaces the message text

All pass with -race.