feat(cli): improve ergonomics with output modes, doctor command, and generated docs

[electather]

Summary

Closes #85

Stacks on #90. Adds three user-facing ergonomics improvements:

1. --output/-o flag — commands that return structured data can now render as json (default), yaml, or table. Proof-of-concept on movies get and search multi; the pattern is documented for future commands.
2. doctor command — runs five checks in order (server configured → reachable → API key configured → API key valid → server version) with short-circuit on failure. Outputs a human-readable table or --output json array.
3. docs generate command — generates full CLI reference as Markdown files using cobra/doc.

Also updates CLAUDE.md with output conventions and seerrclient usage guidance.

Changes

• cmd/apiutil/output.go — OutputMode, AddOutputFlag, GetOutputMode, PrintOutput, PrintRawOutput, table renderer
• cmd/movies/get.go — wired --output flag
• cmd/search/multi.go — wired --output flag
• cmd/doctor/doctor.go + check.go — doctor command with 5 checks, Run() exported for tests
• cmd/docs/docs.go + generate.go — docs generate command
• cmd/root.go — added doctor and docs commands; exempt from server validation in PersistentPreRunE
• tests/output_mode_test.go — 3 new tests
• tests/doctor_test.go — 4 new tests
• CLAUDE.md — output conventions section

Test plan

• go test -v ./... passes
• go fmt ./... produces no diff
• go build succeeds

Manual verification:

seerr-cli doctor
seerr-cli doctor --output json | jq .
seerr-cli movies get 550 --output yaml
seerr-cli movies get 550 --output table
seerr-cli search multi -q "matrix" --output table
seerr-cli docs generate --output-dir /tmp/cli-docs && ls /tmp/cli-docs/

Tests (TDD):

go test -v ./tests/ -run "TestDoctor|TestMoviesGet|TestSearchMultiTable"

Checklist

• New tests added for new behaviour
• Documentation updated (CLAUDE.md, command --help, comments)
• No unrelated changes included