fix(timezone): display API datetimes in Europe/Paris (DST-safe)

[dev-mansonthomas]

Context

Backend datetime fields were historically serialised as naive strings (no TZ designator) and treated as local Paris time by the frontend, which relied on a hardcoded -2h offset in my-slots.component.ts and on Angular's default DatePipe (which uses the browser TZ).

This was wrong twice:

• It broke during DST transitions (CET vs CEST).
• It produced a 2h offset for users outside Paris TZ.

The backend (paired PR rcq-functions-v2 on the same branch name fix/timezone-utc-iso) now serialises every datetime field as strict UTC ISO 8601 with a Z suffix and seconds precision: YYYY-MM-DDTHH:MM:SSZ (no fraction, no offset).

Frontend changes

New ParisDatePipe (src/app/pipes/paris-date.pipe.ts)

Uses Intl.DateTimeFormat with timeZone='Europe/Paris'. Handles:

• ISO strings with Z or explicit offset → parsed as instant.
• Legacy naive strings (no Z, no offset) → re-interpreted as UTC, so the 5-minute Firestore cache window between backend deploy and frontend deploy stays correct.
• Date objects and null / undefined → identity / empty string.
• Format presets: short (dd/MM/yyyy HH:mm), medium, date, time. Falls back to Angular's DatePipe for unknown presets (behavioural compatibility).

Templates migrated to | parisDate

• tronc-history.component.html (depart_theorique, depart, retour)
• tronc-history-dialog.component.html (idem)
• register-tronc-state.component.html (depart_theorique)

my-slots.component.ts

Removed the -2h hack on tronc.depart / tronc.retour. The component now sends new Date(...).toISOString() which produces strict "...Z" strings the backend accepts.

cloud-function.service.ts

parseTroncDates now treats naive legacy strings as UTC (parseAsUtcIfNaive helper) to keep parity with the pipe during the cache window.

shared.module.ts

Declare + export ParisDatePipe so every feature module that imports SharedModule can use | parisDate in templates.

Tests

src/app/pipes/paris-date.pipe.spec.ts covers:

• Summer (UTC+2 / CEST)
• Winter (UTC+1 / CET)
• Legacy naive string
• null / undefined
• Date input
• Unknown preset fallback

Coordination & deploy order

Paired with rcq-functions-v2 PR on the same branch name fix/timezone-utc-iso.

Front-first deploy is safe because the pipe accepts both legacy and ISO formats — once this PR is merged and deployed on the 3 envs, the backend PR can be merged and deployed without any visible regression.

Smoke-test once backend is deployed on dev:

curl -s "https://europe-west1-rq-fr-dev.cloudfunctions.net/historique-tronc-queteur?..." \
  -H "Authorization: Bearer $TOKEN" | jq '.[0].depart'
# -> must end with "Z"

Out of scope

The gcp-deploy.sh indexes subcommand (which unlocked the Mon historique page in the first place) is shipped separately in #140.

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Pull Request opened by Augment Code with guidance from the PR author