P5a plan: PDF documents — seven Ornith tasks with acceptance tests first

docs/plans/p5a: 01 kind+fetch limits, 02 pdftext child + runner, 03 dcache PDF tables,
04 pdfpool, 05 pdfdoc render (map/pages/grep), 06 api, 07 digest citations, metrics, CLI,
skill, unit, README. Given tests compile against a panic-only skeleton and fail there for the
intended reasons; PDFs for tests are built by internal/pdftest (given), plus two qpdf-encrypted
fixtures.

Owner changes for the run: vendor go-pdfkit/extract v0.3.0 + reader v0.6.0 (pinned via
tools.go until task 02); AGENTS.md, tools/run-plan.sh (enforces a Co-Authored-By trailer for
the model), docs/implementer-log.md, `make gate`; gofmt (whitespace) on clean.go and guard;
TestUnsupportedType uses a zip now that PDFs are supported; requestDeadline 90→210 s and
writeTimeout 120→240 s for the PDF path's worst case.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools.go

@@ -0,0 +1,10 @@
+//go:build tools
+
+// Package sift pins the PDF engine chosen for P5a (docs/P5a.md §3) so go.mod and vendor/ carry it
+// before the code that imports it exists. Remove this file once internal/pdftext imports both.
+package main
+
+import (
+	_ "github.com/go-pdfkit/extract"
+	_ "github.com/go-pdfkit/reader"
+)