feat(config): persist the range-resolution timezone

[BramVR]

Outcome

• persist a root timezone config value and add init --timezone, with new configs writing UTC explicitly
• resolve named sync boundaries by --timezone flag, then config, then implicit UTC for legacy configs
• embed IANA timezone data for cross-platform builds; never infer from the machine, Provider, Data Points, locale, or IP
• reject explicit empty or invalid flag/config values before provider calls, archive writes, or setup creation
• expose the resolved timezone through doctor and update the command registry plus generated docs

Closes #403

Proof

• vertical regression coverage for init persistence/rejection, config precedence, legacy UTC, machine-TZ non-inference, doctor output, and pre-effect sync rejection
• go test ./... -count=1
• go test -race ./... -count=1
• make fmt-check and go vet ./...
• repository-pinned lint: 0 issues
• make docs-check and make docs-site
• stamped macOS arm64 binary runtime proof: explicit timezone persisted/reported; empty timezone failed before files existed
• Linux amd64 static binary and Windows amd64 binary cross-build; hosted Linux/Windows execution remains required
• go mod verify and go mod tidy -diff
• reachability vulnerability scan: no vulnerabilities found
• Public Model Identifier Gate and production confidentiality gate: clean
• default structured autoreview and required API-boundary second-engine autoreview: clean

Risk and scope

No schema, migration, provider contract, credential, release, version, tag, or dependency changes. Existing configs without timezone remain UTC. The prior named-range implementation landed in #416 and is the only feature dependency; this PR is scoped to persisted resolution policy and doctor exposure.

[Copilot]

Pull request overview

This PR adds a persisted root timezone configuration and threads that resolved timezone through init, sync preflight, and doctor, while embedding IANA tzdata to ensure cross-platform timezone resolution without relying on machine-local settings.

Changes:

• Add root timezone config persistence (defaulting new configs to explicit UTC) and init --timezone validation.
• Resolve sync named boundaries using precedence --timezone > config timezone > implicit UTC for legacy configs, and validate invalid/empty zones before any provider/archive effects.
• Expose the resolved timezone via doctor output and update command registry + generated docs accordingly.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/googlehealth/range_resolver.go	Embed tzdata and centralize timezone loading/validation for range resolution.
docs/commands/sync.md	Document timezone precedence and updated preflight rejection semantics.
docs/commands/init.md	Document init --timezone and explicit UTC persistence in new configs.
docs/commands/doctor.md	Document doctor reporting of resolved timezone (including legacy UTC).
cmd/gohealthcli/sync_timezone_test.go	Add regression tests for config precedence, legacy UTC behavior, and pre-effect rejection.
cmd/gohealthcli/sync_preflight_gate.go	Add config timezone lookup/caching to preflight and pass resolved timezone into range resolver.
cmd/gohealthcli/sync_preflight_gate_test.go	Update fake preflight context to provide a configured timezone.
cmd/gohealthcli/result_writer_bytes_test.go	Update doctor writer fixtures/expectations to include timezone.
cmd/gohealthcli/init.go	Add --timezone flag, validate it early, and persist to config.
cmd/gohealthcli/init_test.go	Add tests for timezone persistence and early rejection (invalid/empty).
cmd/gohealthcli/doctor.go	Include timezone in doctor JSON/plain/human outputs.
cmd/gohealthcli/doctor_test.go	Add coverage for legacy configs reporting implicit UTC timezone.
cmd/gohealthcli/config.go	Parse root timezone, validate it, and default legacy configs to UTC.
cmd/gohealthcli/commands.go	Update command registry docs for init, sync, and doctor to reflect timezone behavior.

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[Copilot]

Pull request overview

Copilot reviewed 14 out of 14 changed files in this pull request and generated 1 comment.