agency: Style A picked-button treatment (▶ BOLD_UPPER ◀)

[MagMueller]

Picked-button visibility iteration on top of #104.

Symptom

PR #104 shipped a trailing ` ✓` suffix on the picked button. Magnus tested it on his phone, said the mark was technically there but not unmistakable — at phone-button text size, an extra ✓ next to the button's own ✅ blends in. He wanted the entire button to look heavier.

Fix — Style A

Side-by-side comparison of 5 candidate styles posted as cards in TG; Magnus picked Style A: bold uppercase letters wrapped with framing arrows.

Default label	After tap
`✅ Yes`	`▶ ✅ 𝗬𝗘𝗦 ◀`
`⏭ Skip`	`▶ ⏭ 𝗦𝗞𝗜𝗣 ◀`
`✏️ Edit`	`▶ ✏️ 𝗘𝗗𝗜𝗧 ◀`
`Send draft A` (custom)	`▶ 𝗦𝗘𝗡𝗗 𝗗𝗥𝗔𝗙𝗧 𝗔 ◀`

Bold uppercase via Mathematical Sans-Serif Bold (U+1D5D4 onward). Emojis, digits, punctuation pass through unchanged.

Restoring original labels on un-pick

Default kinds use `reset_others=True` — when the user changes their mind, the previously-picked button needs to revert to its original label. That requires knowing the original (we lose case info on bold-uppercase).

Approach: use the suggestion's `buttons_json` from `agency.db` for a lossless restore. When unavailable, fall back to lossy un-bold (case collapses to upper) — fine for the default Yes/Skip/Edit set since "YES" is acceptable.

Legacy mark cleanup

The `✓ ` prefix (PR #103) and ` ✓` suffix (PR #104) mark schemes are still recognized — `_agency_unpick_label` strips them on the next tap so cards posted before this rolled out tidy up automatically.

Test plan

• Tap default Yes/Skip/Edit on a freshly-posted card — picked button shows `▶ ✅ 𝗬𝗘𝗦 ◀` etc., others stay normal
• Re-tap a different default button — previously picked reverts to its original label, new pick shows the bold-arrow treatment
• Tap a custom multi-button card (variant picker) — multiple buttons can wear the picked treatment simultaneously (additive)
• Card posted before this PR (with ` ✓` suffix) gets cleaned up correctly on the next tap

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Summary by cubic

Make picked buttons in agency cards unmistakable by switching to Style A: bold uppercase letters wrapped with arrows. Adds lossless label restore and cleans up legacy checkmark marks.

• New Features
  • Style A transform: "✅ Yes" → "▶ ✅ 𝗬𝗘𝗦 ◀" using Mathematical Sans-Serif Bold; emojis, digits, and punctuation pass through.
  • Default buttons are exclusive (reset others); custom buttons remain additive for stacking actions.
  • Restore original labels on unpick via buttons_json; fallback to un-bold uppercase when missing.
  • Automatically strip old "✓ " prefix and " ✓" suffix marks on the next tap.

^{Written for commit 3b3ff9f. Summary will update on new commits.}