fix(backend): disambiguate duplicate tool names in OrchestratorBlock (#12555)

## Why
The OrchestratorBlock fails with `Tool names must be unique` when
multiple nodes use the same block type (e.g., two "Web Search" blocks
connected as tools). The Anthropic API rejects the request because
duplicate tool names are sent.

## What
- Detect duplicate tool names after building tool signatures
- Append `_1`, `_2`, etc. suffixes to disambiguate
- Enrich descriptions of duplicate tools with their hardcoded default
values so the LLM can distinguish between them
- Clean up internal `_hardcoded_defaults` metadata before sending to API
- Exclude sensitive/credential fields from default value descriptions

## How
- After `_create_tool_node_signatures` builds all tool functions, count
name occurrences
- For duplicates: rename with suffix and append `[Pre-configured:
key=value]` to description using the node's `input_default` (excluding
linked fields that the LLM provides)
- Added defensive `isinstance(defaults, dict)` check for compatibility
with test mocks
- Suffix collision avoidance: skips candidates that collide with
existing tool names
- Long tool names truncated to fit within 64-character API limit
- 47 unit tests covering: basic dedup, description enrichment, unique
names unchanged, no metadata leaks, single tool, triple duplicates,
linked field exclusion, mixed unique/duplicate scenarios, sensitive
field exclusion, long name truncation, suffix collision, malformed
tools, missing description, empty list, 10-tool all-same-name, multiple
distinct groups, large default truncation, suffix collision cascade,
parameter preservation, boundary name lengths, nested dict/list
defaults, null defaults, customized name priority, required fields

## Test plan
- [x] All 47 tests in `test_orchestrator_tool_dedup.py` pass
- [x] All 11 existing orchestrator unit tests pass (dict, dynamic
fields, responses API)
- [x] Pre-commit hooks pass (ruff, black, isort, pyright)
- [ ] Manual test: connect two same-type blocks to an orchestrator and
verify the LLM call succeeds

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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>