[LM-325] Add user attribution (<console-user>@<machine>) to bash Pack…

[Mahesh-Kete]

What

Adds user attribution to the bash Package Firewall MDM scripts: every package-manager
request routed through the firewall is stamped <console-user>@<machine>, so the
firewall log's User column traces to a person — without issuing per-user API keys.
Bash scripts only;

How it works

• Contract (decoded by the backend, LM-326): Basic-auth
  username = base64( base64("userattr:" + label) + ":" + apiKeyId ), password unchanged.
  Attribution is unverified telemetry — never an authorization signal.
• The label only exists on the developer's machine, so credentials are computed at
  install time: generate.sh emits a credentials_block into every generated script.
• Env-expanding tools (npm, yarn berry, maven, poetry) read ${ENDOR_ATTR_USER} /
  secret from ~/.config/endor/env.sh. Literal tools (pip, uv, go — they can't expand
  env vars in their configs) get attributed URLs baked into their config files at install time.
• Shared block files stay Windows-safe: bash swaps the credential references at install
  time (js.sh, maven.sh), with guards that warn if a swap no longer matches.

Hardening included

• generate.sh rejects credential characters that would corrupt generated scripts;
  URL userinfo is percent-encoded on both halves.
• pip: upsert_block now merges into a pre-existing [global] instead of appending a
  duplicate section (pip's configparser rejects duplicates → broken pip). Conflicting keys
  are disabled reversibly (#endor-bak# prefix), including :-delimited keys and indented
  INI continuation lines; endor-remove.sh restores the original config exactly.
  Fixes a pre-existing bug where any machine with existing pip config got a broken pip.
• pip conflict warning retained → MDM alert (exit 1) when existing keys are overridden,
  and persistently for conflicts the merge can't absorb (e.g. index-url under [install]).
• bun: .npmrc username reference swapped to the attributed user — bun resolves
  .npmrc auth last-write-wins, which silently dropped bun's attribution.
• yarn 1.x offboarding: yarn rewrites ~/.yarnrc and can copy the Endor registry
  outside the managed block; endor-remove.sh now deletes exact-match copies of our
  registry line so offboardingfig behind.
• env.sh trimmed to variables with actual runtime readers (dropped dead
  secret-embedding exports).

Testing

• Staging E2E, all 10 tools yarn 2+, bun, pip, uv, poetry,
  go, maven): allowed installs succeed via the firewall, malware-flagged test packages are
  Blocked, and every log rr>@`.
• Offboarding round-trip: endor-remove.sh restores a pre-existing pip.conf
  byte-for-byte, re-enabling the keys it disabled.