Add configurable worktree root

* Add configurable worktree root

Allow new Paseo worktrees to be created under a custom worktrees.root from config.json while preserving the existing PASEO_HOME/worktrees default. Thread the resolved root through create/list/archive/ownership flows, MCP/session paths, checkout metadata, schema, docs, and targeted tests.

* Address worktree root review feedback

Use the resolved Paseo worktree base when a custom PASEO_HOME is provided, and remove an unused worktreesRoot dependency from worktree list handling.

* Fix checkout worktree path test on Windows

Use platform-native paths in the custom PASEO_HOME regression test so Windows CI compares against the same resolved root shape as production code.

* Clarify optional worktrees config docs

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Co-authored-by: Mohamed Boudra <boudra.moha@gmail.com>

packages/website/public/schemas/paseo.config.v1.json

@@ -115,6 +115,16 @@
           },
           "additionalProperties": false
         },
+        "worktrees": {
+          "type": "object",
+          "properties": {
+            "root": {
+              "type": "string",
+              "minLength": 1
+            }
+          },
+          "additionalProperties": false
+        },
         "providers": {
           "type": "object",
           "properties": {