Refactor: structured INPUT parameter availability (Phase 1)

docs/CONTRIBUTING.md

@@ -174,7 +174,7 @@ An practical example is class [LCAO_Deepks](https://github.com/deepmodeling/abac
 
 ABACUS includes a built-in help system that allows users to query INPUT parameters directly from the command line (e.g., `abacus -h ecutwfc`). Parameter metadata is defined inline in the C++ source files (`source/source_io/module_parameter/read_input_item_*.cpp`) using `Input_Item` registrations.
 
-A checked-in file `docs/parameters.yaml` contains a YAML dump of all parameter metadata, generated from the binary itself. This file is used by Sphinx to produce the online documentation page `input-main.md`.
+The C++ `Input_Item` registrations are the source of truth for parameter metadata. The checked-in `docs/parameters.yaml` and `docs/advanced/input_files/input-main.md` files are generated artifacts: do not edit either file manually. `parameters.yaml` is generated from the binary and is used by Sphinx to produce `input-main.md`.
 
 ### When to Update `docs/parameters.yaml`
 
@@ -198,13 +198,13 @@ Then verify the YAML is valid:
 python3 -c "import yaml; d=yaml.safe_load(open('docs/parameters.yaml')); print(len(d['parameters']), 'parameters')"
 ```
 
-You can also regenerate the markdown documentation locally:
+Then regenerate the markdown documentation locally:
 
 ```bash
 python3 docs/generate_input_main.py docs/parameters.yaml --output docs/advanced/input_files/input-main.md
 ```
 
-**Important:** Include the updated `docs/parameters.yaml` and `input-main.md` in your commit when submitting a PR that modifies INPUT parameters. Reviewers should verify the YAML changes match the C++ source changes and the `input-main.md` is updated.
+**Important:** Include the updated `docs/parameters.yaml` and `input-main.md` in your commit when submitting a PR that modifies INPUT parameters. CI regenerates both files from the built binary and rejects any mismatch. Do not fix a documentation mismatch by editing either generated file; update the C++ `Input_Item` registration and regenerate them instead.
 
 ### Parameter Documentation Format
 
@@ -218,7 +218,7 @@ When adding or modifying INPUT parameters in C++ source, set the following field
     item.description = "Description of what this parameter does.";
     item.default_value = "0";
     item.unit = "Ry";          // Optional, empty string if no unit
-    item.availability = "";    // Optional, empty string if always available
+    item.set_availability("basis_type==pw"); // Optional; omit if always available
     // ... read_value, reset_value, check_value functions ...
     this->add_item(item);
 }

docs/developers_guide/agent_governance.md

@@ -220,6 +220,10 @@ or parsing behavior should include both:
 - `docs/parameters.yaml`
 - `docs/advanced/input_files/input-main.md`
 
+These files are generated artifacts, not additional sources of truth. Update
+the C++ `Input_Item` registrations and regenerate both files; do not edit the
+YAML or Markdown output by hand.
+
 If the diff touches parameter internals but does not change user-visible INPUT
 behavior, the PR should state why no documentation update is required. Missing
 documentation updates trigger a governance warning (not a block), but maintainers