feat: add maintainer issue investigation workflow (#665)

* docs: specify issue investigation workflow

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 3732dd5c-330c-4ee4-86e4-0a92eb782e6a

* security: define triage input boundary

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 3732dd5c-330c-4ee4-86e4-0a92eb782e6a

* feat: add issue investigation workflow

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 3732dd5c-330c-4ee4-86e4-0a92eb782e6a

* docs: explain issue investigation command

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 3732dd5c-330c-4ee4-86e4-0a92eb782e6a

* docs: specify investigation discovery hint

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 3732dd5c-330c-4ee4-86e4-0a92eb782e6a

* docs: surface issue investigation command

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 3732dd5c-330c-4ee4-86e4-0a92eb782e6a

* build: regenerate issue triage workflow

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 3732dd5c-330c-4ee4-86e4-0a92eb782e6a

* feat: request missing investigation details

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 3732dd5c-330c-4ee4-86e4-0a92eb782e6a

* fix: harden issue investigation routing

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 3732dd5c-330c-4ee4-86e4-0a92eb782e6a

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* chore: simplify investigation workflows and drop unused PR read

- Tighten prose in issue-investigation and issue-triage workflow prompts
- Restrict GitHub toolset to context,repos,issues (drops pull_requests),
  removing the now-unneeded pull-requests: read agent permission
- Remove docs/superpowers/specs design records from the PR

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 3732dd5c-330c-4ee4-86e4-0a92eb782e6a

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Co-authored-by: Huzaifa Danish <modanish@microsoft.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 3732dd5c-330c-4ee4-86e4-0a92eb782e6a

Author: 4 people