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>

go.mod

@@ -1,9 +1,11 @@
 module git.wntrmute.dev/kyle/sift
 
-go 1.26.0
+go 1.26.4
 
 require (
 	github.com/JohannesKaufmann/html-to-markdown/v2 v2.5.2
+	github.com/go-pdfkit/extract v0.3.0
+	github.com/go-pdfkit/reader v0.6.0
 	github.com/go-shiori/go-readability v0.0.0-20251205110129-5db1dc9836f0
 	github.com/itchyny/gojq v0.12.19
 	github.com/pelletier/go-toml/v2 v2.4.3
@@ -21,6 +23,8 @@ require (
 	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
 	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/go-opentype/opentype v0.12.0 // indirect
+	github.com/go-pdfkit/pdffont v0.3.0 // indirect
 	github.com/go-shiori/dom v0.0.0-20230515143342-73569d674e1c // indirect
 	github.com/gogs/chardet v0.0.0-20211120154057-b7413eaefb8f // indirect
 	github.com/google/uuid v1.6.0 // indirect