UX and visual pass: token chips, measured savings, v0.3.0

[Mattbusel]

• Token boundaries as colored chips (one background per token); indexed grid kept for no-color output.
• The flat "10% savings" guess replaced by a measured number: the tool applies its own phrase and whitespace fixes and re-tokenizes (70 → 61 tokens on the example).
• A file argument no longer opens the tokenizer menu (only pasted text does; the menu accepts typed model names). Header names the tokenizer really used. Warnings to stderr with the fix. --help examples, FORCE_COLOR, emoji removed.
• README rebuilt: pitch, real demo GIF, install table, 3 steps, real results, "which one do I want?" table pointing to tokenviz where it is the better tool. Banner, social preview, example prompt, new tests.

Before (v0.2.0 release binary, same prompt):

After (this branch):