docs: say in the README what termit refuses to do

[tkc]

The README opened with the feature list and never stated the rules that produced it. This writes them down.

The three rules, now in ## Why

• Only what the work needs — a feature has to be something this way of working does not function without. The short list is on purpose.
• A terminal, and nothing more — spawn processes, relay the pty, interpret escape sequences, draw. No conversation management, no driving an agent, no workflows. It is also the reason the agent-specific parts (fork, resume) are a string in the config rather than code in here.
• Measured, not asserted — the lighter option wins, and every speed claim points at a reproducible number, including the ones that were tried and rejected for measuring worse.

## Not goals now says why those things are out — each is either a second way to do what the left pane already does, or a job for a program you run inside a terminal — instead of just listing them.

Corrections while in there

• Hyperlinks (OSC 8) was still listed as no; it has been supported since Open OSC 8 hyperlinks #21.
• Added Synchronized output (?2026), which the parser handles and agent UIs use, to the capability table.
• Linked docs/references/performance-techniques.md and docs/references/scrollback.md from the design notes.
• The size and latency figures now cite the section of docs/performance.md they come from; the binary size stays rounded rather than quoted to a decimal that drifts every build.

No feature text was added: the philosophy section replaces the old "Not a framework" bullet rather than sitting next to it.

🤖 Generated with Claude Code

https://claude.ai/code/session_01GvMacYD6T9EoWqc7C247Hr