feat(time): resolve named sync ranges in IANA timezone

[BramVR]

Outcome

• add sync --timezone <IANA-zone> with UTC fallback and exact now, today, and yesterday inputs
• resolve one captured clock across fan-out into physical, civil, or daily provider boundaries
• preserve explicit date/RFC3339 behavior, exclusive --to, strict preflight, and exact provider-string cursor semantics
• handle 23/25-hour DST days, skipped civil dates, skipped/repeated midnight transitions, fold identity during validation, and fractional physical now
• update the command registry, status conflicts, completion policy, generated command docs, and drift coverage

Closes #402

Proof

• go test ./...
• go test -race ./...
• make fmt-check
• go vet ./...
• pinned repository lint: 0 issues
• make docs-check
• make docs-site
• exact built CLI help + invalid-zone preflight proof
• Windows amd64 binary and test-binary cross-build; hosted Windows execution remains a required PR check
• 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: clean after accepted edge-case fixes
• required API-boundary second-engine autoreview: clean

Risk and scope

No schema, migration, provider write, credential, release, or publication changes. Sync planning resolves once; execution consumes the planned provider strings, and completed-run cursor advancement still stores the exact resolved exclusive --to. Embedded timezone data and persisted config precedence remain scoped to #403; resolved-range status/audit exposure remains scoped to #405.

Dependency freshness was audited without widening this feature PR. Available module updates are unrelated; this change adds no dependency.

[Copilot]

Pull request overview

Adds timezone-aware resolution for named sync range boundaries (now, today, yesterday) so a single captured clock instant can be rendered into provider-appropriate physical/civil/daily boundaries (including DST edge cases) while preserving existing explicit date/RFC3339 behavior and exclusive --to semantics.

Changes:

• Introduces a new range resolver that resolves named boundaries in an explicit IANA timezone (defaulting to UTC) and preserves exact instants for preflight ordering.
• Threads --timezone and a single captured resolvedAt through sync planning/execution so fan-out members share one resolution clock.
• Updates CLI surface area and documentation (flags, --status conflicts, completion tests, and command docs), plus expands test coverage for DST/skipped-date/fold and fractional precision.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/googlehealth/rollup_spec.go	Allows named boundaries through rollup normalization and preserves fractional RFC3339 via RFC3339Nano formatting.
internal/googlehealth/rollup_spec_test.go	Adds coverage to ensure hourly rollup normalization preserves fractional RFC3339 precision.
internal/googlehealth/range_resolver.go	New resolver for named boundaries with IANA timezone handling and target-aware rendering (physical/civil/daily).
internal/googlehealth/range_resolver_test.go	Adds extensive tests for resolver behavior across targets, DST, skipped dates, fold instants, and precision.
docs/commands/sync.md	Documents --timezone and named boundaries semantics, including DST/skipped-date behavior.
cmd/gohealthcli/sync.go	Adds --timezone flag and validates explicitly provided empty timezone.
cmd/gohealthcli/sync_timezone_test.go	End-to-end tests asserting named boundaries reach correct provider filters per target shape and that cursor stores exact resolved --to.
cmd/gohealthcli/sync_status.go	Adds --timezone to the deterministic conflict list for sync --status.
cmd/gohealthcli/sync_status_test.go	Tests --timezone conflict handling with --status.
cmd/gohealthcli/sync_preflight_gate.go	Integrates range resolution into preflight, preserves legacy default-to behavior when applicable, and tightens ordering checks using exact instants.
cmd/gohealthcli/sync_preflight_gate_test.go	Adds tests for local-now resolution, explicit-boundary ordering, DST/fold handling, and shared resolution clock behavior.
cmd/gohealthcli/sync_orchestrator.go	Captures a single resolvedAt once per fan-out invocation when absent.
cmd/gohealthcli/sync_orchestrator_test.go	Tests that one captured range clock is shared across fan-out members.
cmd/gohealthcli/completion_test.go	Adds completion directive coverage for sync --timezone.
cmd/gohealthcli/commands.go	Updates generated command registry text to describe named boundaries + --timezone.

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[Copilot]

Pull request overview

Copilot reviewed 15 out of 15 changed files in this pull request and generated no new comments.