Add terminal E2E control snapshots

tools/TERMINAL_E2E.md

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+# Terminal E2E artifacts
+
+`zig build terminal-e2e` runs `tools/terminal_e2e.py` against the compiled `mim`
+binary and writes ignored artifacts under `.zig-cache/terminal-e2e/<scenario>/`.
+
+Artifact roles:
+
+- `manifest.tsv`: stable scenario facts, hashes, bare-LF status, and artifact list.
+- `visible-controls.normalized.txt`: primary semantic failure artifact. It shows
+  CR as `␍`, LF as `␊`, ESC as `␛`, tabs as `⇥`, and normalizes volatile temp
+  paths.
+- `transcript.txt`: semantic terminal grid after escape/control interpretation.
+- `screenshot.svg` and `terminal.html`: browser-viewable visual evidence.
+- `raw.bin`: exact PTY bytes for low-level debugging.
+
+Golden policy:
+
+- Investigate before updating any expected artifact or assertion.
+- Prefer semantic artifacts (`manifest.tsv`, `visible-controls.normalized.txt`,
+  `transcript.txt`) for assertions; visual artifacts explain what a user would
+  see.
+- Updating artifacts is safe only after the change is intentional and the receipt
+  names the changed UI/control-byte behavior.
+- Bare LF in raw-mode terminal output is a regression unless a scenario explicitly
+  proves a non-raw stream. Raw-mode rendering should use CRLF to avoid diagonal
+  terminal skew.
+- Generated artifacts must remain under ignored build output and must not dirty a
+  clean source tree.