fix: behaviour fixes after the structure rewrite #135

The behaviour fixes deferred during the structure rewrite (#101, merged in #129). The final answer for each item was decided on 2026-10-16; the decisions and their reasons are in #101.

How it runs

• Chunks. The items are grouped into 5 chunks, each tested together on the device in one session. The order is data safety first, then what the next chunk builds on.
• Changelog. Chunk PRs are squash-merged, so each chunk PR's body ends with a BEGIN_COMMIT_OVERRIDE … END_COMMIT_OVERRIDE block listing every fix PR's conventional title. release-please reads it from the merged PR, so the changelog keeps one entry per fix and the right version bump.
• Branches and PRs. Each chunk has its own branch (fix/<chunk>) cut from main. Its item PRs merge there after review and green CI. When the chunk is done, it's tested on the device and the chunk branch merges to main.
• Tests. Tests that pinned the old behaviour (contract PART 1D) change in the chunk that changes that behaviour. Every other test keeps its assertions.
• Where the code goes. Each fix goes to its single owner (see ARCHITECTURE.md); unifying a pair that was co-located in the rewrite means deleting the losing variant.

Chunks

• fix: chunk 1 — files and import safety #136 Chunk 1: files and import safety
• fix: chunk 2 — cockpit membership, file v4 and power zones #131 Chunk 2: cockpit membership, file v4 and power zones
• fix: chunk 3 — link and roster lifecycle, HID #132 Chunk 3: link and roster lifecycle, HID
• fix: chunk 4 — new boards, event log and cockpit actions #133 Chunk 4: new boards, event log and cockpit actions
• fix: chunk 5 — relay, telemetry and the settings form #134 Chunk 5: relay, telemetry and the settings form

Parked for discussion — prioritized 2026-10-18

Kept and filed: #159 (Start with no Gateway starts and waits), #160 ("No nodes reported" with an unadded board on the bus), #161 (Log stream drops rows while paused), #162 ("error-active" label).

Dropped as not critical: Calibration dialog accessible name; stale optional fields on Calibration reopen; Reset… rename offer for a board later added to NODE_IDS.md; "busy" note without a Settings link; Adopt header "0 boards" from a stray's cog; choosing the recording location after Stop; "this file doesn't include…" import preview line; per-board die-temp offset (firmware side).