TreeHouse controllers: run standalone, add the Garage welder

[ii-impy]

What

Re-works the TreeHouse location firmware so every controller holds a fixed look instead of reacting to Garden State, and adds a fifth controller for the Garage welding effect. Rationale is in the new ADR-0021.

Garden State ignored, not removed. Animators run from cg::fullyActive(), so every channel sits at its max_level. Controllers still join WiFi, parse OSC and log it (the heartbeat shows (standalone)). Setting kFollowGardenState in src/main.cpp to true restores the old behaviour.

Location	Look
Dormer	Breathe: a 12.5 s breath between 40% and 80%
Julia	Wander (new): a drunk walk between 40% and 80%, about 60 s per full sweep
Jess	patterns unchanged, now permanently at full drive
Swannatopia	fireplace unchanged; the Chandelier now uses the same warm incandescent spec as the Overhead (it was green)
Garage (new)	arc + 16 px glow, see below

Garage.

• Arc channel. The arc is a new ChannelKind::Trigger: each tap is a 5 ms high pulse on the MOSFET gate, and the cap decides how long the flash lasts.
• Welder timing. lib/Weld's Welder fires taps in three nested random ranges: sessions 8–25 s apart, bursts 1–5 s apart (2–6 per session), taps 20–50 ms apart (1–4 per burst).
• Polling. The Welder is polled every loop() rather than every frame.
• Recharge guarantee. Gaps are measured from the moment a tap actually fires, so a stalled loop can never out-run the cap's recharge.
• Seeding. It is seeded from esp_random() once the radio is up, so the rhythm differs on every boot.
• Glow strip. The new Weld pattern flashes violet-white under each tap, then cools through orange to dark. Each tap adds heat, so long bursts glow longer.
• Pins. kArcPin and kGlowPin in garage.h are placeholders.
• Self-test. garage-selftest taps once at the start of each colour phase, then fires a four-tap, 40 ms burst at the start of white.
• Network. treehouse_garage is at 192.168.1.64 in network.json, net_config.h is regenerated, and the Garage is added to the Pi's locations.controllers.

Related to #44 (Pi-side reactivity); this PR doesn't close any issue.

Verification

• pio test -e native: 47/47 pass (14 new: test_weld, plus breathe, wander, weld-glow and fully-active cases)
• pio run for all 10 hardware envs (5 locations + 5 self-tests): all build, no warnings
• make test in .venv: 266 passed
• Not yet run on hardware: the pins, the 5 ms pulse width and the cap recharge timing all need bench confirmation

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