Diagnostics: Only deliver discovery reports that carry a mapping

[d4rken]

What changed

The "Help add support" wizard no longer produces reports that a maintainer can't act on.

• It now asks for the battery-protection feature name and your software version before you start capturing, instead of leaving both optional.
• If switching modes changed no settings at all, there's no longer a way to send the result. The step explains the likely causes and offers a restart.
• If settings did change but none are included in the report, sending is blocked until at least one row is included, with an explanation of the reveal step. Withholding individual rows still works exactly as before.

Also adds a support-assistant knowledge file for Amply under docs/support/.

Technical Context

Prompted by the first device-support email to reach support@darken.eu: a HONOR report with changed_rows=0, feature_name=unspecified and rom_version=unspecified. Nothing was broken. PR #31 shipped in 0.2.1-beta0 and behaved as designed: it blocks a single-capture session and warns on an empty matrix, but deliberately let an empty two-mode result through, because "this ROM keeps the mode somewhere else" is a real finding. The report was delivered via the app's own "Send by email instead" button, so the contributor followed the flow correctly.

That #31 decision is reversed here. The negative result is real but indistinguishable from the two capture mishaps that produce identical output, so it was never trustworthy enough to justify the reports it admitted.

Two commits:

1. detailsComplete gates DETATLS -> CAPTURE. Those two fields are the only part of a report that survives a zero-diff capture and often identify the ROM family on their own, so they move ahead of CAPTURE rather than sitting optional on a step users skip. Whitespace-only input doesn't count.
2. deliverable (review.any { it.included }) gates REVIEW -> DELIVER, covering both dead ends with one predicate: an empty matrix leaves review empty, an all-withheld matrix leaves nothing included. nothingIncluded distinguishes the fixable case so the second card can name the reveal step. The contribution_next_empty ("Continue anyway") string is gone.

Worth a look during review: the all-withheld gate is the one with a real cost. A new OEM's key is redacted by default, so this is the normal state of the highest-value reports, and the gate pushes on people who may have stopped out of uncertainty. It does not force disclosure of any particular row, and the two-stage reveal/include model is unchanged.

ContributionReport.formatContributionReport keeps its zero-row wordings. They're now unreachable from the wizard but the formatter is a pure, separately-tested function and the schema-2 output stays correct.

docs/support/kindmail-system-prompt.md is content for the support mail assistant, not app code. It's here because it documents Amply's device-support matrix and discovery-report triage, both of which drift with the adapters. It records that zero-setting reports can now only come from 0.2.1-beta0 or older. It also overrides the shared prompt's Pro/refund/Play-rating sections, none of which apply to a pre-launch app with no billing.