fix(cli): validate --repo filter on gitt issues list (#1061)

[RUNECTZ33]

Fixes #1061. Reopened from PR #1113 — that one targeted `main` instead of `test` and was closed (CONTRIBUTING.md says branches should target `test`). This is the same diff, rebased onto current upstream/test (`9b620da`), tests adjusted for the test-branch's network-header-in-JSON-mode behavior.

Problem

`--repo <owner/name>` on `gitt issues list` (added in #910) compares raw user input directly against `repository_full_name`:

```python
issues = [
i for i in issues
if i.get('repository_full_name', '').lower() == repo_filter.lower()
]
```

So:

• Malformed inputs like `ownerrepo` or `owner//repo` are silently accepted and quietly match nothing (no error feedback).
• Whitespace-padded valid inputs like `' entrius/gittensor '` fail to match real entries because the comparison string still contains the surrounding spaces.

Fix

Reuse the existing `validate_repository(verify_exists=False)` helper before any contract read. It already:

• strips whitespace,
• enforces the `owner/repo` regex,
• raises `click.BadParameter` with `param_hint='--repo'` on bad input.

Surface that exception through the existing `handle_exception` path so JSON consumers get a structured `bad_parameter` error and human callers exit non-zero — same shape used by `--id` validation a few lines above.

The same validator is already used by mutating commands (`gitt issues register/cancel` in `mutations.py`), so the read-side `--repo` filter now matches the documented contract enforced everywhere else in the CLI.

Tests added

6 new tests in `tests/cli/test_issues_list_json.py`:

• Malformed filters rejected with structured `bad_parameter` error in JSON mode (parametrized over `ownerrepo`, `owner//repo`, `owner/`, `/repo`, `owner repo`).
• Malformed filters exit non-zero in human mode.
• Whitespace-padded valid filter `' owner/repo '` correctly matches contract entries.
• Mixed-case filter `OWNER/REPO` still matches (preserves existing case-insensitive behavior).
• Valid non-matching filter returns empty list, not all issues.

Tests use a small `_parse_json_payload(output)` helper that slices from the first `{` so they're robust whether `print_network_header` writes to stdout in JSON mode (current test branch) or not.

All 19 tests in the file pass; `read_issues_from_contract` is asserted not-called for invalid input so we never burn a contract read on bad parameters.

Diff size

• `gittensor/cli/issue_commands/view.py`: +13 lines (1 import + 11-line validation block)
• `tests/cli/test_issues_list_json.py`: +95 lines (6 new tests + helper)
• Total: +108 lines, 0 deletions, 2 files

[anderdc]

the issue was close as not completed, we are not pursuing it