test(bitcoin-only): gate unsupported 7.15 handlers

[BitHighlander]

Firmware PR BitHighlander/keepkey-firmware#620 repaired its full/Bitcoin-only CI invocations, which exposed two tests that sent intentionally stripped handlers to the Bitcoin-only image.

This adds the existing full-feature capability gate to:

• the BIP-85 class, whose handler is not linked into the Bitcoin-only product
• the native MAYA memo-shape test, whose handler is likewise full-feature-only

Exact failing evidence on firmware CI run 33021365730 was GetBip85Mnemonic: Unknown message and MayachainSignTx: Unknown message. Bitcoin product-boundary tests themselves passed.

[BitHighlander]

CI triage:

• integration-btc passes and directly reproduces the product variant this PR fixes.
• The full-feature gate is a no-op on the full image, so these two added calls do not alter any full test execution.
• The full integration job reported seven failures in untouched suites: 2 Binance unknown-message cases, 1 EOS frozen-hash mismatch, and 4 Solana AdvancedMode disclosure cases. None is in either file changed by this PR.
• Firmware PR #620 is independently rerunning its own full and Bitcoin-only matrices with this exact companion commit at run 33022901199.

Accordingly, the full companion-lane failures are recorded as existing harness/firmware selection debt, not caused by this two-line capability-boundary change. I will still wait for the authoritative firmware matrix before merging the firmware stack.

[BitHighlander]

Follow-up commit c697a25115ea859ab5b0a89f77dd2c77e61ab889 closes the report-accounting failure exposed by firmware CI:

• the Bitcoin-only run had 269 passed, 415 skipped, and zero JUnit failures
• only four full-product Solana LUT entries were incorrectly marked skipped-but-required
• the validator is now explicitly variant-aware
• regression tests prove the full product still fails if those four tests skip, while Bitcoin-only accepts their intentional absence

Firmware #620 now passes KK_FIRMWARE_VARIANT=bitcoin-only to the report container and is awaiting its PR-attached rerun at head c0546655.

[BitHighlander]

Exact-head CI disposition for c697a25:

• integration-btc: passed
• lint: passed
• Both new report-variant regression tests passed in the full job: full product rejects skipped Solana LUT coverage; bitcoin-only accepts the intentionally absent Solana LUT handlers.
• The full integration job seven failures exactly match the already documented incompatible baseline: 2 Binance Unknown message, 1 EOS hash mismatch, and 4 Solana AdvancedMode failures. No new failure was introduced by this patch.

This PR is therefore ready for its scoped purpose: capability-gating the 7.15 Bitcoin-only companion suite and validating its variant-specific report catalog.