docs/build: define v0.7 episode semantics research boundary

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Summary

• Add ADR 0001 for v0.7 episode semantics research boundaries.
• Record the current activity_segments plus best-window behavior and the continuous-background/two-dense-peaks limitation as a research fixture target, without changing v0.6 detector behavior.
• Enable -Wall -Wextra -Wpedantic for GCC/Clang and /W4 for MSVC on LogLens-owned targets.
• Keep warnings-as-errors off for ordinary builds and enable -Werror / /WX only for project-owned targets in CI, CodeQL, fuzz smoke, and the ci-release preset.

Validation

• MSVC strict Release build with LOGLENS_WARNINGS_AS_ERRORS=ON.
• MSVC CTest: 6/6 passed.
• WSL/GCC strict Release build with -Wall -Wextra -Wpedantic -Werror.
• WSL/GCC CTest: 6/6 passed.
• Generated project policy checks: default targets use Level4 without Werror; CI targets use Level4 with TreatWarningAsError.
• actionlint, JSON parse, local ADR link checks, git diff --check, and privacy path scan passed.

Review protocol

• Design decision: keep v0.6 episode behavior unchanged; make v0.7 fixture/oracle research explicit before selecting a density-aware algorithm.
• Main risk: future warning additions may vary across compiler versions; strictness is deliberately scoped to CI and LogLens-owned targets.
• Compatibility impact: no runtime/report behavior changes; local consumers can disable warnings with LOGLENS_ENABLE_WARNINGS=OFF.
• Rollback path: revert the three commits or disable the CMake warning options without touching detector/report contracts.
• Issues Backlog: decide configurable semantics for privilege auth failure signals #100–Backlog: evaluate report surface for non-counting auth signals #102 are outside this change.