Salvages the four pure-Termux / install-UX commits from #21433 onto current main. Excludes the three commits in that PR that touched desktop-impacting code paths (TUI markdown list rendering, cli.py resize scrollback behavior, browser_tool lightpanda fallback logic, and a doctor.py venv-preference reorder). Those were bundled into #21433 under a title that only described the heartbeat change — they deserve their own scoped PRs.

Commits (all @adybag14-cyber)

• fix(update): add heartbeat during dependency install — wraps the three subprocess.run dep-install calls in _install_python_dependencies_with_optional_fallback with a 30s elapsed-time heartbeat thread so hermes update doesn't look frozen during silent Rust/C build phases. Universal benefit, Termux-motivated.
• fix: strengthen termux install network prerequisites — adds check_network_prerequisites() to scripts/install.sh that probes pypi + duckduckgo with curl before trying pkg installs; adds ca-certificates curl to the Termux package list; Termux-gated guidance on failure.
• fix: add termux-all install profile and safe fallbacks — adds a new [termux-all] extra in pyproject.toml that bundles the extras known to resolve on Android (excludes matrix + voice which have broken Android wheels). Additive; doesn't touch existing [termux] or [all].
• feat: add termux doctor fallback guidance for blocked extras — 14-line addition to doctor.py with Termux-specific fallback hints when an extra is unavailable.

Not included from #21433

Left to contributor to resubmit as separate scoped PRs if desired:

• fix(termux): preserve CLI scrollback and harden lightpanda open fallback — removes \x1b[3J from ALL platforms' resize recovery (not Termux-gated). Also refactors lightpanda→Chrome fallback URL logic for every user.
• fix(tui): stabilize list/url wrapping in assistant markdown — changes TUI+dashboard markdown list rendering globally. Needs embedded-TUI dashboard smoke test, not just messages.test.ts.
• fix(termux): prefer active .venv and reduce doctor noise — reorders venv detection for every desktop user from (venv, .venv) to (active, .venv, venv). Defensible but cross-platform and deserves its own review.

Validation

scripts/run_tests.sh tests/hermes_cli/test_update_autostash.py tests/hermes_cli/test_doctor.py \
  tests/test_install_sh_termux_network_prereqs.py tests/test_termux_all_extra_compat.py \
  tests/hermes_cli/test_update_yes_flag.py tests/hermes_cli/test_cmd_update.py
# 76 passed

git log --diff-filter=A origin/main..HEAD --stat  # No stray files outside termux/install scope

Closes #21433.