Adds a new CLI flag that filters out GitHub template repositories
from search results. Template repos are marked with is_template in
the GitHub API response.

- Add isTemplate: boolean to CodeMatch in types.ts
- Map is_template from GitHub API in api.ts
- Add excludeTemplates param to aggregate() with guard
- Thread excludeTemplates through output.ts (ReplayOptions,
  buildReplayCommand, buildOutput)
- Add excludeTemplates param to runInteractive() in tui.ts
- Register --exclude-template-repositories CLI flag and wire through
  searchAction in github-code-search.ts
- Add shell completion entry in completions.ts
- Add unit tests for the new filter in aggregate.test.ts
- Update docs: filtering.md, cli-options.md, README.md

Closes #116

- types.ts: make isTemplate optional (isTemplate?: boolean) to keep
  existing builders/fixtures valid without changes
- output.ts: shell-quote groupByTeamPrefix in buildReplayCommand
  to prevent replay command breakage when the value contains spaces
- output.test.ts: add tests for excludeTemplates flag in replay command;
  update groupByTeamPrefix assertion to reflect new shell-quoting
- docs/usage/filtering.md: fix intro count (three → four filtering
  options); reword template info box to clarify filtering applies in
  both interactive and non-interactive mode

- output.ts: shell-quote --org arg in buildReplayCommand for safety
  (org names with spaces/metacharacters could break the replay command)
- output.test.ts: update --org assertion to expect quoted value
- docs/usage/filtering.md: reword intro from 'pre-query filtering
  options' to 'result filtering options' since --include-archived and
  --exclude-template-repositories act after fetching, not before

- aggregate.ts: use strict === true check for isTemplate (field is
  optional; falsy on undefined would silently skip the guard)
- output.ts: shell-quote --exclude-extracts values in buildReplayCommand
  (file paths can contain spaces or shell metacharacters)
- output.test.ts: update assertions to expect quoted values