feat(pagination): expose page param on list-query tools

[ysyneu]

Problem

The list-query MCP tools hit paginated Flashduty backends (ListOptions{Page, Limit}) but exposed only limit (max 100). Any result past the first page was unreachable — a query matching >100 items silently dropped the tail, with no recourse but narrowing the time window/filters. The truncated/hint machinery even flagged the shortfall while offering no way to page.

Fix

Add a 1-based page param to every list tool that queries a Page-capable endpoint and surfaces a total:

Tool	Change
query_incidents	+ page
query_changes	+ page
query_incident_alerts	+ page (applied per incident)
query_channels	+ limit + page
query_members	+ limit + page
query_teams	+ limit + page

Dedicated by-ID lookups that return everything stay unpaged (incident_ids→list-by-ids, person_ids→person/infos, team_ids→team/infos). channel_ids is a filter on the same paginated /change... /channel/list, so it pages like any listing.

Truncation-signal correctness

addTruncationHint compared total > count (this page's size) — correct only on page 1. On a final partial page it falsely reported truncated and sent the agent chasing an empty next page. New addPageHint accounts for the page offset (seen = (page-1)*limit + count) and names the exact next page. Full-set / by-ID responses keep addTruncationHint.

change_ids correctness

/change/list has no server-side id filter, so query_changes(change_ids=…) filters one page client-side. It now reports total = found count and skips the page hint (feeding the filtered count with the window's unfiltered total into addPageHint would mislead: "Showing 0 of 5000, request page:2").

Consistency

Shared optionalPaging helper centralizes the limit/page parse across the six handlers (also removes a stray hardcoded 20 in query_changes); PageDescription mirrors LimitDescription.

Out of scope

list_similar_incidents — backend /incident/past-list has no Page (top-N by design).

Tests

pagination_page_test.go: wire-level tests that page reaches the backend as p (and default omits it), the channel_ids/person_ids path split, the change_ids found-count/no-hint behavior, and a table-driven TestAddPageHint covering the last-page math.

go build, go vet, and go test ./pkg/... ./internal/... all pass. (make lint fails locally on a golangci-lint↔go toolchain version mismatch, unrelated to this change.)