feat(train): interval plans, synced and sealed, with an editor and templates (ADR 0030, D42)

Train's server gains the synced `plan` table, a sealed payload alone;
the migration `plans` only adds it, its space index and the foreign key
to its sync space, and a person's deletion takes it with their space.

The app keeps plans as `plan` rows sealed for their row: a name, what
they are for, whether a step off target is told, and blocks of steps
repeated, each ending after a time, a distance or a lap tap and aiming
at a pace, speed, heart rate or zone, or the rower's split, watts or
stroke rate. Home's Plans tab lists them, a new one starts from nothing
or from a template (4×4 minutes, Tabata, 10×400 m), the editor changes
steps on a sheet, and a deletion asks first and can be undone.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

docs/adr/0030-halkyon-train.md

@@ -1,10 +1,10 @@
 # ADR 0030: Halkyon Train, what it does and where its data comes from
 
-- **Status:** decided 27–28 Oct 2026, by the developer (D1–D41 below). The shell (D12)
+- **Status:** decided 27–28 Oct 2026, by the developer (D1–D43 below). The shell (D12)
   is built; recording (D13–D28) is built on Android, iOS waiting for a Mac; Health
   Connect (D29–D31) is built; the Loop's setup and keeping (7a, D34–D36) and its
   daily data (7b, D37, D38), its sessions (7c, D39) and its firmware (D10, D40) are
-  built, and its live heart rate (7d, D41).
+  built, and its live heart rate (7d, D41); intervals (D42, D43) are being built.
 - **Numbering:** 0025 is held by the federation draft (stashed), 0026–0029 by the .NET
   rewrite on the local branch `rewrite-dotnet`, abandoned on 27 Oct; Train takes the next
   free number so that neither is ever read as this one.
@@ -801,6 +801,34 @@ Strava. What was found, 27 Oct:
   nor a Loop is there. Not yet tried with a Loop: whether its live rate needs the
   band in a mode of its own, and how far the wrist's rate lags a strap's.
 
+- **D42 Interval plans, and who runs them** (recommended, the developer's; 28 Oct): a plan
+  is a name and a list of steps (warm-up, work, recovery, cool-down) with repeat
+  blocks; each step ends after a time, after a distance, or with a lap tap, and may
+  aim at a target: a pace or speed range (from GPS), a heart-rate range in bpm or one
+  of five zones, and on the rower a split, watts or a stroke rate (over pace and heart
+  rate alone). The zones are Polar's and most watches': 50–60, 60–70, 70–80, 80–90 and
+  90–100 % of the profile's highest heart rate, its default from age where unset, as
+  for the band (over Karvonen's heart-rate reserve, which needs a resting rate). Plans
+  are Train's synced, sealed `plan` rows, so one made on the desktop reaches the
+  phone (over the person's folder alone), with an editor and a few templates to start
+  from (4×4 min, Tabata 8×20/10 s, 10×400 m; over none). The recording service runs
+  the plan, sent to it as the recording starts: it moves from step to step on its own
+  moving time and distance, pauses stopping a step's clock, and writes `step` lines
+  to the recording file, which the app reads (over the open app running it, which
+  Android may stop with the screen off). Every step change gives a tone, a vibration
+  and, where the phone has a text-to-speech engine (GrapheneOS ships none; RHVoice or
+  eSpeak from F-Droid give one), a spoken line naming the step, its length and its
+  target; a timed step counts its last three seconds down; off target, a short cue at
+  most every 30 s, switchable per plan (over tones alone, and over no off-target
+  cues). A step on the rower doesn't set its resistance yet (over setting it through
+  FTMS's control point): whether the WP 5000 speaks FTMS is still unknown (D8).
+- **D43 What an interval workout keeps** (recommended, the developer's; 28 Oct): the
+  workout keeps the plan's name and its steps as run, a lap each (when, how long, how
+  far), sealed in its payload; its page lists each step with its time, distance,
+  average pace or speed and heart rate, on the rower its split and watts, marked where
+  it held its target, and shades the charts by step (over laps without targets, and
+  over no trace of the plan).
+
 ## Consequences
 
 - Train's sensors are one pattern: open profiles read by the app itself, on the phone;