Adds an `upgrade` subcommand that walks a project from anthropic 0.x to
1.x (httpx2 HTTP layer, Python 3.10 floor, removed deprecated surface).
- New python/claude-api/sdk-upgrade.md: scope and version check, a
greppable inventory of affected call sites, one section per breaking
change, verification, and a report format.
- SKILL.md: `upgrade` subcommand row and a reading-guide entry.
- python/claude-api/README.md: timeouts use anthropic.Timeout, custom
clients note httpx2, link to the SDK MIGRATION.md.
- shared/live-sources.md: SDK major-version upgrade guides table.
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