docs: Getting Started + three worked examples (crono / liftoff / withings)

[Terastar-Paperclip]

Summary

• GETTING_STARTED.md — zero-to-first-export guide; covers install (Homebrew + build-from-source), prime, auth per CLI, date flags, --format, and how to run the conformance suite. Links to CONTRACT.md and compat/README.md.
• docs/example-crono.md — crono-export worked example: credentials, prime output, nutrition export, food-log jq recipe, biometrics query, flag-validation demonstration, compat suite run.
• docs/example-liftoff.md — liftoff-export worked example: OAuth login, prime output, workouts list, bodyweight trend, compat suite run (parse-level; data-path skipped pending CI credential provisioning).
• docs/example-withings.md — withings-export worked example: OAuth login, prime output, activity/sleep/measurements exports, full compat suite run (stub server + fake token; all §4 cells machine-attested).

Verification

All commands executed at HEAD against locally built binaries:

go build -o /tmp/crono-export crono-export-cli
go build -o /tmp/liftoff-export liftoff-export-cli
go build -o /tmp/withings-export withings-export-cli
EXPORT_CLI_BIN=/tmp/crono-export go test -tags=compat ./...   # ok
LIFTOFF_EXPORT_BIN=/tmp/liftoff-export go test -tags=compat ./...  # ok
WITHINGS_EXPORT_BIN=/tmp/withings-export go test -tags=compat ./... # ok

CONTRACT.md citations are verbatim (grep-verified). No fabricated §X references.

Content lenses applied

• Inverted pyramid: lede names audience + outcome in one sentence per page.
• Worked-example primacy: commands before explanations.
• Recognition over recall: exact env var names, flag values, and exit codes shown.
• Progressive disclosure: GETTING_STARTED.md covers the 80% path; deep config in prime and CONTRACT.md.

Reviewer

Awaiting DT (board) approval click. Shared GH identity means self-approval is blocked.