[BUG] Copilot target writes userPromptSubmit; Copilot's event is userPromptSubmitted, so prompt hooks never run

Describe the bug
A package hook on UserPromptSubmit (or userPromptSubmit) installed for the
copilot target is written to .github/hooks/*.json under the key
"userPromptSubmit". Copilot CLI has no event by that name, so the hook never
runs and nothing is logged.

Copilot's hooks reference
(https://docs.github.com/en/copilot/reference/hooks-configuration) names the
camelCase event userPromptSubmitted. Its PascalCase UserPromptSubmit is the
VS Code-compatible variant, which switches the payload to snake_case.

Cause: _HOOK_EVENT_MAP["copilot"] in
src/apm_cli/integration/hook_integrator.py:

"UserPromptSubmit": "userPromptSubmit",
"userPromptSubmit": "userPromptSubmit",

tests/integration/test_hook_integrator_copilot_casing_e2e.py asserts the
same wrong name.

To Reproduce

1. A package pkg with apm.yml (target: [copilot]) and .apm/hooks/x.json:
   {"hooks":{"UserPromptSubmit":[{"hooks":[{"type":"command","command":"echo hit >> hook.log"}]}]}}
2. A project that depends on pkg, with target: [copilot]. Run apm install.
   .github/hooks/pkg-x.json holds "userPromptSubmit".
3. Start copilot in the project and send a prompt. No hook.log is written.
4. Change the key to "userPromptSubmitted" in the deployed file, restart
   copilot and send a prompt. hook.log contains hit.

Expected behavior
apm writes userPromptSubmitted for the copilot target, and the hook runs on
every prompt.

Environment

• OS: Windows 11 (pwsh 7)
• APM Version: 0.31.0. The same map is on main at 98616b9.
• GitHub Copilot CLI 1.0.86

Additional context
Related: #2111 (hook semantics), whose comment table already lists
userPromptSubmitted for Copilot. The reverse direction is not covered here:
a Copilot-authored userPromptSubmitted package installed for claude, codex
or kiro passes through unrenamed. That can be a separate issue if wanted.

Sending fix in a PR: map the three spellings to userPromptSubmitted for
copilot target, correct the tests and add a CHANGELOG entry.

I checked two points before you post:

• The file name in step 2 is unverified. I read the deployed file with a wildcard (.github/hooks/.json), so I never saw its actual name. pkg-x.json follows the pattern from the earlier probe, where the file was pkg-herdr-tab-label.json. Either write .github/hooks/.json in step 2, or let me rerun the install and get the real name.
• The template's "Python Version" field is left out. apm here is the installed binary, not something I ran through a Python interpreter.

Start in src/apm_cli/integration/hook_integrator.py at _HOOK_EVENT_MAP["copilot"], then read tests/integration/test_hook_integrator_copilot_casing_e2e.py. Update the Copilot event mapping, adjust the assertions, and add the requested CHANGELOG entry. Done means the generated .github/hooks/*.json uses userPromptSubmitted and the Copilot casing test passes.