chore: point release automation at the renamed main branch

[cleanunicorn]

The repository default branch was renamed master → main. This updates everything that still pointed at the old name.

Changes

• .github/workflows/release.yml: push.branches [master] → [main]. Without this, no release would ever be cut again.
• pyproject.toml: [tool.semantic_release.branches.main].match "(main|master)" → "main".
• docs/deploy.md: all master references updated; corrected the stale pyproject.toml:64-66 line reference to 82-84.

Not changed (on purpose)

• CHANGELOG.md — historical entries, left as written.
• master in llama.cpp / ggml URLs (src/drove/model_config.py, src/drove/gguf.py) — those are external repos with their own default branch.

Verified

• All four workflow files parse as valid YAML; pyproject.toml parses and resolves to {'main': {'match': 'main'}}.
• install.yml already targeted [main], so its push trigger was dead on the old default branch and starts working again with the rename.
• No open PRs targeted master at rename time.

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