Monetization: add a "Buy Me a Coffee" patron option alongside Pro #160

Context
From the Nov 1, 2026 feedback triage: paid upgrades / donations, with the base app staying free, was an open discussion item with no issue filed. Pro is one monetization leg (Pro-gated features behind the pro flag, e.g. music in #105). This issue files the second leg: a patron / donation path.

Ask
Add a "Buy Me a Coffee"-style patron option as another way for users to support Toastmusters, in addition to Pro — not instead of it, and not paywalling the base timer.

Open questions (decide before building)

• Platform: Buy Me a Coffee, Ko-fi, GitHub Sponsors, or another? (One platform to start.)
• One-time tips only, or recurring patron tiers? What, if anything, do patrons get — recognition, or nothing but thanks?
• Where it lives: landing page, in-app (settings / about), timer report footer, or all three? Keep it low-key so it never reads as a paywall.
• How it is presented alongside Pro so the two options do not compete or confuse (Pro = features, patron = support).

Acceptance

• A patron link/button is live in the agreed spot(s), pointing at the chosen platform.
• Base timer stays fully free; no feature is moved behind the patron option.