Add bisect_ppx test coverage infrastructure with CI workflow and test suites

Integrate bisect_ppx for code coverage across the test suite:

- Add bisect_ppx instrumentation to lib/dune and test/dune
- Add bisect_ppx dependency to dune-project, nixtamal.opam, and nix/package/nixtamal.nix
- Create bisect.yml configuration for HTML and text coverage reports
- Add .github/workflows/coverage.yml for CI-based coverage reporting
- Fix flake.nix devShell to include checkInputs for full development environment
- Add coverage checks to flake.nix checks output

New test suites for recently ported features:
- test/test_upgrade.ml: Tests for schema upgrade command (backup, dry-run, version validation)
- test/test_fossil.ml: Tests for Fossil VCS codec and lockfile roundtrips
- test/test_lockfile.ml: Tests for lockfile auto-creation and serialization
- test/test_main.ml: Register all new test suites

Documentation updates:
- AGENTS.md: Add contact info (website, XMPP MUC), note llm/ folder is gitignored
- README.asciidoc: Add website link, mention Fossil VCS, schema versioning, upgrade command
- .gitignore: Add _build/ and _coverage/ directories

Covers testing for previously ported features: schema upgrade, Fossil VCS support,
and lockfile auto-creation.

1 files changed, 6 insertions, 1 deletions

diff --git a/README.asciidoc b/README.asciidoc
index 607f02e..921e96e 100644
--- a/README.asciidoc
+++ b/README.asciidoc
@@ -9,6 +9,7 @@
 /nɪks.təˈmal/ ("nix-tamal")
 
 Maker:: toastal
+Website:: https://nixtamal.tech (launching soon)
 
 Put out:: 2026
 
@@ -30,7 +31,7 @@ Nixtamal is a tool to pin input version like its predecessors niv, npins, Pinch,
 
 * keeps a stable reference pin to supported VCSs
 * supports mirrors for fetching [1]
-* supports patch-based VCSs, like Pijul & Darcs, in a first-class sense (tho nixpkgs will be required due to Nix builtins fetchers limitations)
+* supports patch-based VCSs, like Pijul, Darcs, & Fossil, in a first-class sense (tho nixpkgs will be required due to Nix builtins fetchers limitations)
 * uses a KDL manifest file with templating instead of CLI input
 * supports arbitrary commands for getting the latest change for inputs
 * refreshes inputs; skips frozen
@@ -40,6 +41,7 @@ Nixtamal is a tool to pin input version like its predecessors niv, npins, Pinch,
 * source code & community will never be hosted on a proprietary, privacy-invasive, megacorporate platform with obligations to shareholders or venture capital
 * licensed for your freedom
 * ML-family programming (feels closer to Nix)
+* supports schema versioning for manifests and lockfiles
 
 Future goals (planned but not yet implemented):
 
@@ -136,6 +138,7 @@ Opens text editor. & After editing …
 ----
 $ nixtamal lock
 $ nixtamal refresh
+$ nixtamal upgrade
 ----
 
 === What next?
@@ -305,6 +308,8 @@ For details read LICENSE.txt with full license texts at license/.
 
 Currently this is best done by sending a patchset to toastal+nixtamal@posteo.net or DM me a remote to clone @ toastal@toastal.in.th.
 
+Website: https://nixtamal.tech
+
 Community is in an XMPP MUC (chatroom) with future hopes to have an IRC gateway. Join @ xmpp:nixtamal@chat.toastal.in.th?join.
 
 Additionally, please read the PITCHING_IN.rst file for other information/expectations.