docs: remove stale browser docs, unused assets and history wording

[arzafran]

What this does

Agents reading SKILL.md were told to run programa browser ..., which stopped existing when the built-in browser was removed. This points them at Aside instead, and clears out the docs, images and scripts that still described removed features. About 12 MB of unused images go with it.

Summary

• SKILL.md: the browser section now routes everything through Aside.
• docs/removed/README.md: fills in the browser row's line count (35,000) and drops the browser from the "core kept" list.
• Deleted docs/plans/browser-developer-tools.md (plans for removed code). rust-core-concepts.md section 11 links to the removal docs.
• Deleted .github/workflows/test-depot.yml (manual-only, unused, half a copy of test-e2e.yml) and scripts/measure-glass-memory.sh (no callers).
• Deleted 13 images with no reference anywhere in the repo.
• OSC 7501 comments in ProgramStatus.swift, AgentActivityStateTests.swift and the tests_v2 test now cite docs/program-status.md instead of the deleted plan.
• .gitignore: removes a duplicate node_modules rule and the exception for a plan that only explained removed mobile code.
• scripts/run-tests-v2.sh: the guard keyed to user cmux on cmux-vm becomes an explicit PROGRAMA_TESTS_V2_VM=1 opt-in, since the script kills running Programa instances.
• Comments in workflows, scripts, docs and tests_v2 reworded to describe the current state instead of its history.

No Swift behavior changes; the three Swift edits are comments.

Test plan

• python3 scripts/check-settings-docs.py passes
• python3 scripts/check-structural-budgets.py passes
• git grep for each deleted file's basename returns nothing outside CHANGELOG and docs/removed
• CI is green