feat(docs): improve devx, fix Makefile targets (#32237)

**TL;DR much of the provided `Makefile` targets were broken, and any
time I wanted to preview changes locally I either had to refer to a
command Chester gave me or try waiting on a Vercel preview deployment.
With this PR, everything should behave like normal.**

Significant updates to the `Makefile` and documentation files, focusing
on improving usability, adding clear messaging, and fixing/enhancing
documentation workflows.

### Updates to `Makefile`:

#### Enhanced build and cleaning processes:
- Added informative messages (e.g., "📚 Building LangChain
documentation...") to makefile targets like `docs_build`, `docs_clean`,
and `api_docs_build` for better user feedback during execution.
- Introduced a `clean-cache` target to the `docs` `Makefile` to clear
cached dependencies and ensure clean builds.

#### Improved dependency handling:
- Modified `install-py-deps` to create a `.venv/deps_installed` marker,
preventing redundant/duplicate dependency installations and improving
efficiency.

#### Streamlined file generation and infrastructure setup:
- Added caching for the LangServe README download and parallelized
feature table generation
- Added user-friendly completion messages for targets like `copy-infra`
and `render`.

#### Documentation server updates:
- Enhanced the `start` target with messages indicating server start and
URL for local documentation viewing.

---

### Documentation Improvements:

#### Content clarity and consistency:
- Standardized section titles for consistency across documentation
files.
[[1]](diffhunk://#diff-9b1a85ea8a9dcf79f58246c88692cd7a36316665d7e05a69141cfdc50794c82aL1-R1)
[[2]](diffhunk://#diff-944008ad3a79d8a312183618401fcfa71da0e69c75803eff09b779fc8e03183dL1-R1)
- Refined phrasing and formatting in sections like "Dependency
management" and "Formatting and linting" for better readability.
[[1]](diffhunk://#diff-2069d4f956ab606ae6d51b191439283798adaf3a6648542c409d258131617059L6-R6)
[[2]](diffhunk://#diff-2069d4f956ab606ae6d51b191439283798adaf3a6648542c409d258131617059L84-R82)

#### Enhanced workflows:
- Updated instructions for building and viewing documentation locally,
including tips for specifying server ports and handling API reference
previews.
[[1]](diffhunk://#diff-048deddcfd44b242e5b23aed9f2e9ec73afc672244ce14df2a0a316d95840c87L60-R94)
[[2]](diffhunk://#diff-048deddcfd44b242e5b23aed9f2e9ec73afc672244ce14df2a0a316d95840c87L82-R126)
- Expanded guidance on cleaning documentation artifacts and using
linting tools effectively.
[[1]](diffhunk://#diff-048deddcfd44b242e5b23aed9f2e9ec73afc672244ce14df2a0a316d95840c87L82-R126)
[[2]](diffhunk://#diff-048deddcfd44b242e5b23aed9f2e9ec73afc672244ce14df2a0a316d95840c87L107-R142)

#### API reference documentation:
- Improved instructions for generating and formatting in-code
documentation, highlighting best practices for docstring writing.
[[1]](diffhunk://#diff-048deddcfd44b242e5b23aed9f2e9ec73afc672244ce14df2a0a316d95840c87L107-R142)
[[2]](diffhunk://#diff-048deddcfd44b242e5b23aed9f2e9ec73afc672244ce14df2a0a316d95840c87L144-R186)

---

### Minor Changes:
- Added support for a new package name (`langchain_v1`) in the API
documentation generation script.
- Fixed minor capitalization and formatting issues in documentation
files.
[[1]](diffhunk://#diff-2069d4f956ab606ae6d51b191439283798adaf3a6648542c409d258131617059L40-R40)
[[2]](diffhunk://#diff-2069d4f956ab606ae6d51b191439283798adaf3a6648542c409d258131617059L166-R160)

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

docs/scripts/kv_store_feat_table.py

@@ -1,9 +1,6 @@
 import sys
 from pathlib import Path
 
-from langchain_community import document_loaders
-from langchain_core.document_loaders.base import BaseLoader
-
 KV_STORE_TEMPLATE = """\
 ---
 sidebar_class_name: hidden

docs/scripts/notebook_convert.py

@@ -175,8 +175,23 @@ def _modify_frontmatter(
 def _convert_notebook(
     notebook_path: Path, output_path: Path, intermediate_docs_dir: Path
 ) -> Path:
-    with open(notebook_path) as f:
-        nb = nbformat.read(f, as_version=4)
+    import json
+    import uuid
+
+    with open(notebook_path, "r", encoding="utf-8") as f:
+        nb_json = json.load(f)
+
+    # Fix missing and duplicate cell IDs before nbformat validation
+    seen_ids = set()
+    for cell in nb_json.get("cells", []):
+        if "id" not in cell or not cell.get("id") or cell.get("id") in seen_ids:
+            cell["id"] = str(uuid.uuid4())[:8]
+        seen_ids.add(cell["id"])
+
+    nb = nbformat.reads(json.dumps(nb_json), as_version=4)
+
+    # Upgrade notebook format
+    nb = nbformat.v4.upgrade(nb)
 
     body, resources = exporter.from_notebook_node(nb)