TaskGroup type + GitHub sub-issue detection + group state

[hsubra89]

Resolves #77

Automated implementation by rlph.

[hsubra89]

Review Summary

3 warnings found that need code changes before merge. 10 informational items noted for optional improvement.

Warnings (must fix)

• .gitignore L29 — tracked config with dev branch: .rlph/config.toml was removed from .gitignore and is now committed with base_branch set to a development branch name. This looks unintentional — re-add it to .gitignore and remove the tracked file.
• src/sources/github.rs L186 — inconsistent label case-sensitivity: Sub-issue label matching uses exact equality (l.name == self.label) while is_gql_eligible (L117) uses eq_ignore_ascii_case for status labels. Apply eq_ignore_ascii_case consistently for label matching on lines 186 and 210 to avoid silent filtering mismatches.
• src/sources/github.rs L179 — child_ids from ineligible parents suppress standalone tasks: child_ids are collected from ALL top-level issues (including ones with in-progress/in-review/done labels). If a parent has an exclusion label, its sub-issues are added to child_ids but the parent is skipped at L201. Sub-issues that also appear as top-level issues are then suppressed at L198, making them unselectable as standalone tasks. Only collect child_ids from parents that pass the eligibility check.

Info (optional improvements)

• src/deps.rs L18: Regex recompiled on every parse_dependencies call — consider static LazyLock<Regex>.
• src/deps.rs L77: Mixed ref/deref destructuring style in .filter(|&(_, deg)| *deg == 0).
• src/sources/github.rs L46: (*header).into() → header.to_string().
• src/sources/github.rs L125: parse_gql_issue and parse_gql_sub have near-identical bodies — could share a helper.
• src/sources/github.rs L145: _impl suffix is uncommon; fetch_task_groups_via_graphql conveys intent better.
• src/sources/github.rs L209: Chained .filter().filter() could be a single .filter().
• src/sources/github.rs L219: .map(|si| Self::parse_gql_sub(si)) → .map(Self::parse_gql_sub).
• src/sources/mod.rs L59: all_sub_issue_ids on Standalone returns the task's own ID — add a doc comment clarifying this choice.
• src/state.rs L25: CurrentGroupState fields have redundant group_ prefix (e.g., group.group_id → group.id).

[hsubra89]

The warning about external dependency blocking is outdated — commit 8ba7586 removed the group_ids filter from next_eligible_sub_issue. The current code at src/sources/mod.rs:109-110 checks all deps against done_ids, and the test test_group_next_eligible_external_dep_blocks (line 337) verifies external deps block correctly.

[hsubra89]

The external dependency blocking warning is now resolved — commit 8ba7586 removed the group_ids.contains(d) filter so all deps (including external) are checked against done_ids. The test test_group_next_eligible_external_dep_blocks confirms the fix.