refactor(R2d.108): convert mountAIRoutes to AIHandlers struct field-bag

Replace 54 positional `*AI<Name>Handler` parameters on mountAIRoutes

with a single `h AIHandlers` struct param. Each struct field is typed

as `http.Handler` (interface) so subsequent parallel subpackage carves

(R2d.109+) can move concrete AI handler types into per-feature subpkgs

without re-touching the mountAIRoutes signature on every carve — only

the router.go field assignment changes, which already conflicts on

every router-touching carve.

Mechanical rewrite:

  - 54 `aiXxx` body refs -> `h.Xxx` (126 substitutions total via

    word-boundary regex pass that excluded `aiXxxStubHandler` because

    word boundaries don't split between `aiChatbot` and `Stub`)

  - mountAIRoutes signature: 60 lines of positional params collapsed

    to one `h AIHandlers` param

  - router.go call site: 54-positional one-liner expanded to struct

    literal with explicit field names so future field additions don't

    silently corrupt order

  - stale Parameters: doc-comment block on mountAIRoutes shortened

    (the AIHandlers struct fields are self-documenting)

Gates green: go build ./..., go vet ./..., go test ./internal/arch

./internal/api ./internal/api/..., archmetrics compare, golangci-lint

run ./internal/api/....

Unblocks parallel AI carve fleet (batch 10, ~50 agents) — each agent

moves one AI handler to its own subpkg + flips one struct-field type

in router.go without ever touching ai_routes.go.

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

Author: atulmgupta