docs: use ko-fi.com/cotabby and trim the tagline

[FuJacob]

Follow-up to #638, which merged before these two edits had landed on the branch. Net change is two lines:

• Switch the Ko-fi link to ko-fi.com/cotabby.
• Trim the tagline to "Open-source, on-device AI autocomplete for macOS."

🤖 Generated with Claude Code

Greptile Summary

This PR makes two minor copy edits to README.md as a follow-up to #638.

• Replaces the Ko-fi donation link (ko-fi.com/I2F22066MI) with the canonical project page (ko-fi.com/cotabby), making the URL easier to remember and verify.
• Shortens the tagline from the full two-clause sentence to just "Open-source, on-device AI autocomplete for macOS."

Confidence Score: 5/5

Two-line documentation change — safe to merge.

Both edits are cosmetic README copy changes. The Ko-fi URL swap points to the canonical project page and the tagline trim removes the redundant second clause. No code, logic, or configuration is touched.

No files require special attention.

Important Files Changed

Filename	Overview
README.md	Updates Ko-fi donation link from a personal hash URL to the canonical ko-fi.com/cotabby page, and trims the tagline to its first clause.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[README.md] --> B[Tagline]
    A --> C[Ko-fi donation link]
    B --> B1["Before: full two-clause sentence"]
    B --> B2["After: 'Open-source, on-device AI autocomplete for macOS.'"]
    C --> C1["Before: ko-fi.com/I2F22066MI"]
    C --> C2["After: ko-fi.com/cotabby"]

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