Port upstream patches: Cmdliner 2.x, lockfile auto-creation, schema upgrade, Fossil VCS

Ported from upstream darcs repository (v1.1.2):
- Cmdliner 2.x compatibility fixes (variable shadowing)
- Lockfile auto-creation when missing
- Schema upgrade command with backup/rollback
- Fossil VCS support (new VCS type)
- Clean up Cmdliner warning for unescaped $PWD

Files modified:
- lib/schema.ml (new): Schema versioning module
- lib/nixtamal.ml: Add upgrade function, Fossil meld support
- lib/error.ml: Add Fossil to prefetch_method, Upgrade error
- lib/input.ml: Add Fossil module, Kind variant
- lib/prefetch.ml: Add Fossil prefetch with SRI hash support
- lib/manifest.ml: Add Fossil codec
- lib/lockfile.ml: Add Fossil lockfile type
- lib/lock_loader.ml: Add Fossil feature flag
- lib/input_foreman.ml: Add Fossil display and prefetch check
- bin/cmd.ml: Cmdliner 2.x fixes, add Upgrade command
- bin/dune, lib/dune, test/dune: Deprecation flags

Builds successfully with all tests passing.

1 files changed, 1 insertions, 0 deletions

diff --git a/bin/main.ml b/bin/main.ml
index bdb25e7..739776f 100644
--- a/bin/main.ml
+++ b/bin/main.ml
@@ -27,6 +27,7 @@ let cmd ~env =
 		Cmd.Lock.cmd ~env;
 		Cmd.List_stale.cmd ~env;
 		Cmd.Refresh.cmd ~env;
+		Cmd.Upgrade.cmd ~env;
 	]
 	in
 	Cmdliner.Cmd.group info subcommands