feat(tasks): support reminder write via dot-notation (v1.2.0)

- Add reminder_unit, reminder_value to create_task
- Add reminder_unit, reminder_value, clear_reminder to update_task
- Wire format verified: reminder.reminderUnit / .reminderValue /
  .reminderType (SNOOZE=active, NONE=clear) / .localId (optional)
- Valid units: MINUTE, HOUR, DAY (WEEK rejected by enum decoder)
- Clear requires full inactive block; partial updates reject with
  "task reminder invalid"
- Flat top-level keys, JSON string and bracket notation are silently
  ignored by the server — confirmed via isolated fuzz per variant
- Update SPEC.md, CLAUDE.md, README.md, CHANGELOG.md
- Remove outdated "not supported" warning in update_task docstring

CHANGELOG.md

@@ -10,6 +10,34 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 This project follows Semantic Versioning (SemVer).
 Breaking changes (removed tools, changed parameters) increment the major version.
 
+## [1.2.0] – 2026-04-17
+
+### Added
+- **Reminder write support** for `create_task` and `update_task`:
+  - `reminder_unit`: `"MINUTE"`, `"HOUR"`, or `"DAY"`
+  - `reminder_value`: non-negative integer (e.g. `30` for "30 minutes before")
+  - `clear_reminder` (update_task only): remove reminder
+- The correct wire format uses **dot-notation** subfields
+  (`reminder.reminderUnit`, `reminder.reminderValue`, `reminder.reminderType`,
+  `reminder.localId`) — flat top-level keys, JSON-string, and bracket-notation
+  are silently ignored by the server.
+
+### Fixed
+- `update_task` docstring: removed the "reminders not supported" warning — the
+  v1.1.2 write format was flat, which the FiZ encoder silently drops; the
+  dot-notation variant works on both Free and Premium accounts.
+
+### Investigation notes (2026-04-17)
+- Verified via isolated fuzz test (fresh test task per variant): only dot-notation
+  succeeds; every other encoding is accepted with HTTP 200 and `lastAction: UPDATED`
+  but the reminder remains at default `{reminderType: NONE, reminderValue: 0}`.
+- `reminder.localId` is optional.
+- Partial block updates (e.g. only `reminder.reminderType=NONE`) return
+  `task reminder invalid` — the full inactive block must be sent to clear.
+- Valid `reminderUnit` values: `MINUTE`, `HOUR`, `DAY`. `WEEK` is rejected by the
+  API enum decoder.
+- Reminder + recurrency can be set in a single `taskupdate2` call without interference.
+
 ## [1.1.2] – 2026-04-17
 
 ### Fixed